APPARATUS AND METHOD FOR EXCAVATING A CAVITY AND SETTING AN OBJECT AT LEAST PARTIALLY THEREIN Field The present disclosure relates to an apparatus and method for excavating a cavity and setting an object at least partially therein. Definition In the specification the term "comprising" shall be understood to have a broad meaning similar to the term "including" and will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. This definition also applies to variations on the term "comprising" such as "comprise" and "comprises". Background The digging, or excavating, of holes and trenches into the ground and the setting of objects at least partially therein is frequently required. For example, it may be desired to set into the ground a tree root barrier installation, a pit installation (such as a service pit), a service conduit (such as an electrical, gas, water or communications conduit) or a post (such as a post for a sign or a streetlight, a power line post or a telephone line post). The present inventor has ascertained that an improvement in the speed, efficiency and/or cost of at least some such operations is desirable and has developed a method and apparatus for performing at least some such operations and providing one or more of the above improvements or at least providing a useful alternative to known methods and apparatus. 1 Summary According to a first aspect of the present disclosure there is provided an apparatus for excavating a cavity and setting an object at least partially therein, the apparatus comprising: a vehicle on which are mounted: a suction generator for providing suction for moving material to be excavated from a bed of material in order to provide a cavity; a chamber for receiving said material, the chamber having an inlet for ingress of said material; and a lifting and setting apparatus for lifting the object and moving the object at least partially into the cavity. In an embodiment the apparatus further comprises a conduit for passage of said material to the inlet. In an embodiment the lifting and setting apparatus comprises a base and a first elongate support member pivotally coupled to the base. In an embodiment the lifting and setting apparatus comprises a second elongate support member pivotally coupled to the first elongate support member. In an embodiment the lifting and setting apparatus comprises a third elongate support member pivotally coupled to the second elongate support member. In an embodiment the support members are drivable to pivot about their pivotal couplings by one or more powered actuators. In an embodiment the support members are drivable to pivot about their pivotal couplings by at least one of: one or more hydraulic actuators; one or more pneumatic acuators; one or more cables. 2 In an embodiment the lifting and setting apparatus is capable of lifting a weight of at least 500 kg at a horizontal distance from the base of at least four meters. In an embodiment the lifting and setting apparatus is capable of lifting a weight of at least 700 kg at a horizontal distance from the base of at least four meters. In an embodiment the lifting and setting apparatus is capable of lifting a weight of at least 900 kg at a horizontal distance from the base of at least six meters. In an embodiment the lifting and setting apparatus is capable of lifting a weight of at least 900 kg at a horizontal distance from the base of at least eight meters. In an embodiment the lifting and setting apparatus comprises a crane. In an embodiment the lifting and setting apparatus comprises a loader crane. In an embodiment the lifting and setting apparatus comprises an arrangement for restricting undesired movement of the object. In an embodiment the arrangement for restricting undesired movement of the object comprises an arrangement for retaining part of the object close to, or in contact with a jib or arm of the lifting and setting apparatus. In an embodiment the arrangement for restricting undesired movement of the object comprises an arrangement to hold the object. In an embodiment the arrangement to hold the object is adapted to extend at least partially around part of the object. In an embodiment the arrangement to hold the object bears less than half the weight of the object when the object is lifted by the lifting and setting apparatus. In an embodiment the arrangement to hold the object comprises first and second jaws, relatively moveable to selectively hold or release the object. 3 In an embodiment the lifting and setting apparatus comprises a grapple for holding and manipulating said object. In an embodiment the lifting and setting apparatus comprises a pole grapple for holding and manipulating said object when said object comprises a pole. In an embodiment the apparatus comprises a fluid storage compartment for storing a fluid for supply to a lance which can be used for loosening material to be excavated. In an embodiment the fluid storage compartment comprises a storage tank provided on the vehicle. In an embodiment the fluid storage compartment comprises a fluid storage part of a container which at least partially defines the chamber. In an embodiment said fluid storage part being is partitioned from the chamber to prevent or restrict mixing of excavated material with fluid stored for supply to a lance. In an embodiment the apparatus comprises a pressuriser for pressurising fluid for supply to a lance which can be used for loosening material to be excavated. In an embodiment the apparatus comprises a lance for loosening material to be excavated. In an embodiment the lance is of a type which expels gas or liquid under pressure. In an embodiment the lance is of a type which expels a liquid which is mainly water. In an embodiment the vehicle comprises a motorised vehicle. In an embodiment the vehicle comprises a trailer. In an embodiment the vehicle further comprises a motorised vehicle to which the trailer is connected. In an embodiment the vehicle comprises a truck. 4 In an embodiment the chamber and the lifting and setting apparatus are mounted on the truck. In an embodiment the chamber and a mounting of the lifting and setting apparatus are spaced apart in a longitudinal direction of the vehicle. In an embodiment the lifting and setting apparatus is attached to a chassis of the vehicle. In an embodiment the chamber is attached to a chassis of the vehicle. In an embodiment the lifting and setting apparatus is mounted closer to a rear of the vehicle than is the chamber. In an embodiment the lifting and setting apparatus is mounted closer to a front of the vehicle than is the chamber. In an embodiment the chamber comprises a door which is openable to facilitate removal of material from the chamber. In an embodiment the door is provided at a lateral side of the chamber. In an embodiment the door is provided at a rear end of the chamber. In an embodiment the vehicle comprises a tipping arrangement to tip the chamber in order to facilitate removal of material from the chamber. In an embodiment the vehicle provides an intermediate storage region, for storing and transporting items, the intermediate storage region being provided between the chamber and a longitudinal position at which the lifting and setting apparatus is mounted on the vehicle. In an embodiment the storage region comprises at least part of a deck region of a truck. In an embodiment the vehicle provides a side storage region, for storing and transporting items, the side storage region being provided at or adjacent a side of the chamber. 5 The side storage region may be provided in the form of the interior of a container provided at or adjacent a side of the chamber. In an embodiment the vehicle provides a base storage region, for storing and transporting items, the base storage region being provided below a deck of the vehicle and/or adjacent part of the chassis of the vehicle. In an embodiment the base storage region is provided substantially below the chamber. The base storage region may be provided in the form of the interior of a container provided below said deck of the vehicle and/or adjacent said part of the chassis of the vehicle. In an embodiment the apparatus further comprises at least one support, mountable on the vehicle, for supporting an object to be set in a cavity. In an embodiment the apparatus further comprises at least two spaced apart supports for supporting an object to be set in a cavity. In an embodiment at least one support for supporting an object to be set in a cavity comprises a support surface, positioned above a deck portion of the vehicle, for supporting said object. In an embodiment the support surface defines at least one recess for receiving at least part of said object. In an embodiment at least one support for supporting an object to be set in a cavity comprises a cradle. In an embodiment at least one support for supporting an object to be set in a cavity comprises a cradle for supporting a pole. In an embodiment the apparatus comprises at least two spaced apart supports for supporting a pole. 6 In an embodiment the lifting and setting apparatus is arranged so that it can lift said object from said at least one support. In an embodiment the lifting and setting apparatus is arranged so that it can be positioned in a storage configuration in which at least one elongate arm member thereof extends longitudinally in a substantially longitudinal direction of the vehicle. In an embodiment the suction generator and the chamber have a common power source. In an embodiment the common power source comprises the engine of the vehicle. In an embodiment the common power source comprises a power take off provided by the vehicle. In an embodiment the common power source comprises a livedrive provided by the vehicle. In an embodiment the vehicle is provided with an auxiliary ignition switch for allowing the engine of the vehicle to be started from outside a cab of the vehicle. The auxiliary ignition switch may be mounted on the vehicle. The auxiliary ignition switch may be provided on a remote control unit which provides a wireless control signal to start the engine of the vehicle. In an embodiment the common power source comprises an auxiliary engine provided on the vehicle, but which does not provide motive power for the vehicle. In an embodiment the vehicle comprises a hydraulics system. In an embodiment the hydraulics system comprises at least one auxiliary output to allow connection and operation of detachable hydraulic tools. In an embodiment the vehicle comprises a pneumatics system. 7 In an embodiment the pneumatics system comprises at least one auxiliary output to allow connection and operation of detachable pneumatic tools. In an embodiment controls for both the lifting and setting apparatus and the suction generator are provided on the vehicle. In an embodiment controls for the lifting and setting apparatus are provided on a remote control unit. In an embodiment controls for the suction generator are provided on a remote control unit. In an embodiment controls for both the lifting and setting apparatus and the suction generator are provided on a single remote control unit. According to a second aspect of the present disclosure there is provided a method of excavating a cavity and setting an object at least partially therein comprising: providing a vehicle on which are mounted: a suction generator for providing suction of material to be excavated from a bed of material in order to provide a cavity; a chamber for receiving excavated material, the chamber being connected to a conduit for passage of material from said bed of material to said chamber; and a lifting and setting apparatus for lifting and moving said object; moving the vehicle to a location where it is desired to set said object at least partially within a cavity; excavating a cavity suitable for receipt of the object, by operating the suction generator in order to provide suction and using said suction to pass material from said bed of material through the conduit into the chamber; and 8 moving the object using the lifting and setting apparatus so that the object is set at least partially within the cavity. In an embodiment excavating the cavity comprises use of a lance to loosen material from the bed of material to facilitate passage of the material through the conduit. In an embodiment the lance is of a type which expels gas or liquid under pressure to loosen material from the bed of material. In an embodiment the lance is of a type which expels a liquid which is mainly water, to loosen material from the bed of material. In an embodiment the method comprises no substantial movement of the vehicle between excavating the cavity and moving the object using the lifting and setting apparatus so that the object is set at least partially within the cavity. In an embodiment the vehicle comprises a motorised vehicle. In an embodiment the vehicle comprises a trailer. In an embodiment the vehicle further comprises a motorised vehicle to which the trailer is connected. In an embodiment the vehicle comprises a truck. In an embodiment the method comprises transporting a crew for performing the method to the location where it is desired to set said object at least partially within a cavity, within the vehicle. In an embodiment the method comprises using only crew who were transported within the vehicle to the location where it is desired to set said object at least partially within a cavity, at said location. 9 In an embodiment the method comprises using the vehicle to transport just one worker substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises said one worker, without assistance from any additional on-site worker: excavating the cavity suitable for receipt of the object, by operating the suction generator in order to provide suction and using said suction to pass material from said bed of material through the conduit into the chamber. In an embodiment the method comprises said one worker, without assistance from any additional on-site worker: moving the object using the lifting and setting apparatus so that the object is set at least partially within the cavity. In an embodiment the method comprises using the vehicle to transport at least two workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises said at least two workers, without assistance from any additional on-site worker: excavating the cavity suitable for receipt of the object, by operating the suction generator in order to provide suction and using said suction to pass material from said bed of material through the conduit into the chamber. In an embodiment the method comprises said at least two workers, without assistance from any additional on-site worker: moving the object using the lifting and setting apparatus so that the object is set at least partially within the cavity. In an embodiment the method comprises using the vehicle to transport a crew of three, and only three, workers substantially to the location where it is desired to set said object at least partially within a cavity. 10 In an embodiment the method comprises using the vehicle to transport a crew of at least three workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises using the vehicle to transport a crew of four, and only four, workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises using the vehicle to transport a crew of at least four workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises using the vehicle to transport a crew of five, and only five, workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises using the vehicle to transport a crew of at least five workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises using the vehicle to transport a crew of six, and only six, workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises using the vehicle to transport a crew of at least six workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises using the vehicle to transport a crew of seven, and only seven, workers substantially to the location where it is desired to set said object at least partially within a cavity. 11 In an embodiment the method comprises using the vehicle to transport a crew of at least seven workers substantially to the location where it is desired to set said object at least partially within a cavity. In an embodiment the method comprises said crew transported using the vehicle, without assistance from any additional on-site worker: excavating the cavity suitable for receipt of the object, by operating the suction generator in order to provide suction and using said suction to pass material from said bed of material through the conduit into the chamber. In an embodiment the method comprises said crew transported using the vehicle, without assistance from any additional on-site worker: moving the object using the lifting and setting apparatus so that the object is set at least partially within the cavity. In an embodiment the method comprises transporting one or more additional workers, in one or more additional vehicles, substantially to the location where it is desired to set said object at least partially within a cavity, so that the one or more additional workers are at said location for at least some of the time during which said one or more workers transported by said vehicle are at said location. In an embodiment at least one of the one or more additional vehicles is a passenger car or ute (pick-up truck). In an embodiment all of the one or more additional vehicles is a passenger car or ute (pick up truck). In an embodiment at least one of the one or more additional vehicles is a passenger vehicle having not more than eight seats or a goods vehicle having a mass not exceeding 3.5 tonnes. In an embodiment all of the one or more additional vehicles is a passenger vehicle having not more than eight seats or a goods vehicle having a mass not exceeding 3.5 tonnes. 12 In an embodiment at least one of the one or more additional vehicles is a vehicle to which is mounted an adjustable height elevated working platform. In an embodiment the method comprises transporting the object substantially to the location where it is desired to set said object at least partially within a cavity, using the vehicle. In an embodiment the object comprises a pole. In an embodiment the object comprises a pole for supporting at least one electrical conductor. In an embodiment the object comprises a pit. In an embodiment the object comprises a valve. In an embodiment the object comprises a pipe or a section of pipe. In an embodiment the object comprises a foundation. In an embodiment the object comprises a precast concrete foundation. In an embodiment the method comprises transporting a plurality of objects, each of which is to be set at least partially within a cavity, using the vehicle. In an embodiment the method comprises: excavating a first cavity suitable for receipt of a first of the plurality of objects, by operating the suction generator in order to provide suction and using said suction to pass material from said bed of material through the conduit into the chamber; moving the first of the plurality of objects using the lifting and setting apparatus so that the first of the plurality of objects is set at least partially within the cavity; excavating one or more respective subsequent cavities for one or more respective subsequent objects of the plurality of objects, by operating the suction generator in order to 13 provide suction and using said suction to pass material through the conduit into the chamber; and moving the one or more respective subsequent objects of the plurality of objects, using the lifting and setting apparatus, to be set at least partially within the one or more respective subsequent cavities. In an embodiment the method is a replacement method comprising replacing an object which is set at least partially within a cavity. In an embodiment the replacement method comprises excavating around the object to be replaced to facilitate removal of the object to be replaced. In an embodiment the replacement method comprises excavating around the object to be replaced by operating the suction generator in order to provide suction and using said suction to pass material from around the object to be replaced through the conduit into the chamber In an embodiment the replacement method comprises removing the object to be replaced from the position in which it was set at least partially within a cavity. In an embodiment removing the object to be replaced comprises use of the lifting and setting apparatus. In an embodiment removing the object to be replaced comprises use of at least one additional piece of equipment. In an embodiment said at least one additional piece of equipment comprises a pole jack. In an embodiment the setting and lifting apparatus may be engaged with the object to be replaced prior to completing excavating around the object to be replaced. In an embodiment the setting and lifting apparatus may be engaged with the object to be replaced prior to commencing excavating around the object to be replaced. 14 Engaging the setting and lifting apparatus with the object to be replaced prior to completing (and/or commencing) excavating around the object to be replaced, can assist in preventing inadvertent movement (or toppling) of the object to be replaced. In an embodiment the excavating of a cavity suitable for receipt of the object, by operating the suction generator in order to provide suction and using said suction to pass material from said bed of material through the conduit into the chamber, comprises enlarging a cavity left when the object to be replaced is removed. In an embodiment the excavating of a cavity suitable for receipt of the object, by operating the suction generator in order to provide suction and using said suction to pass material from said bed of material through the conduit into the chamber, comprises excavating a cavity close to the object to be replaced, prior to removing the object to be replaced. In an embodiment the replacement method comprises a method of replacing a pole with a replacement pole. The replacement pole may be a pole which is secured to a foundation. In this case the object to be set at least partially within a cavity may be the foundation. In an embodiment the method comprises use of an apparatus in accordance with one or more of the embodiments of the first aspect, set out above. According to a third aspect of the present disclosure there is provided an object which has been set at least partially within a cavity using an apparatus in accordance with the first aspect of the present disclosure. According to a fourth aspect of the present disclosure there is provided a transmission arrangement comprising a plurality of cable supports and at least one transmission cable supported above the ground by said cable supports, wherein at least one of the cable supports comprises an object in accordance with the third aspect of the present disclosure. 15 In an embodiment at least one of the cable supports comprises a pole. In an embodiment the transmission cable comprises a cable for transmission of electrical current. In an embodiment the transmission cable comprises a cable for transmission of telecommunications data. According to a fifth aspect of the present disclosure there is provided an object set at least partially within an excavated cavity, which cavity has been excavated and which object has been set at least partially therein by a method of excavating a cavity and setting an object at least partially therein in accordance with the second aspect of the present disclosure. According to a sixth aspect of the present disclosure there is provided a transmission arrangement comprising a plurality of cable supports and at least one transmission cable supported above the ground by said cable supports, wherein at least one of the cable supports comprises an object in accordance with the fifth aspect of the present disclosure. In an embodiment at least one of the cable supports comprises a pole. In an embodiment the transmission cable comprises a cable for transmission of electrical current. In an embodiment the transmission cable comprises a cable for transmission of telecommunications data. It will be appreciated that features and characteristics set out in relation to any one of the above aspects may be applicable to other aspects. Brief description of the drawings Embodiments will be described below, in detail, with reference to accompanying drawings. The primary purpose of this detailed description is to instruct persons having an interest in the subject matter of the invention how to carry the invention into practical effect. However, 16 it is to be clearly understood that the specific nature of this detailed description does not supersede the generality of the preceding broad description. In the accompanying diagrammatic drawings: Figure 1 is a schematic side view of an embodiment of an apparatus for excavating a cavity and setting an object at least partially therein, in accordance with the present disclosure; Figure 2 is a schematic perspective view from the rear, above and left-hand side, of a variation of the embodiment of Figure 1; Figure 3 is a schematic perspective view from the rear and right-hand side, of the embodiment of Figure 2; Figure 4 is a schematic perspective view from the front and right-hand side, of the embodiment of Figures 2 and 3; Figure 5 is a schematic perspective view from the front and right-hand side, of the embodiment of Figures 2 to 4 in use, setting a pole into an excavated cavity; and Figure 6 is a schematic view of an embodiment of part of a crane suitable for use in the embodiments of Figures 1 to 5, showing an arrangement for restricting undesired movement of a pole being lifted by the crane; Figures 7(a) and 7(b) illustrate schematically an embodiment of a crane suitable for use in the embodiments of Figures 1 to 5, showing a compact configuration and an extended configuration, respectively; and Figures 8(a) to 8(j) is a sequence illustrating schematically stages in a method of replacing a pole with a new pole using an embodiment of an apparatus in accordance with the present disclosure. 17 Detailed description of embodiments With reference to Figure 1, an embodiment of an apparatus for excavating a cavity and setting an object at least partially therein, in the form of an excavating/setting apparatus, is generally designated 1. The excavating/setting apparatus 1 comprises a truck 10, on which are mounted a suction generator, in the form of a vacuum unit 12 for providing suction, and a chamber, in the form of a spoils tank 14, for receiving excavated material. In this embodiment the vacuum unit comprises a positive displacement blower. However, it will be appreciated that any suitable alternative suction generator or vacuum unit could be used, for example, suitable vacuum units may comprise a suction pump (for example a liquid ring pump or a vane pump). The spoils tank 14 has an inlet 16 for ingress of excavated material and an outlet 18 connected to the suction vacuum unit 12 by a suction conduit 20 (shown schematically in Figure 1, as in a more practicable arrangement the suction conduit would be run lower, and on the side of the apparatus which is not visible in Figure 1.). The excavating/setting apparatus 1 further comprises a lifting and setting apparatus, which in this embodiment comprises a crane 22 for lifting and moving an object which is to be set in a cavity. In Figure 1 the crane 22 is shown in a compact configuration, suitable for storage and transportation. In this embodiment, in the compact configuration, the crane is arranged so that it extends in the width direction of the truck 10. This provides a storage region 24 of a deck of the truck 10 which can be used for transporting objects to be set into cavities, and sundry additional apparatus which may be useful in the excavating/setting operations, such as augers and pole setters (not shown). In this embodiment the excavating/setting apparatus 1 further comprises an inlet conduit 26 for passage of excavated material, under suction, to the inlet 16. 18 Further, in this embodiment, the spoils tank 14 is of the type that has a rear door 28, pivotable about a hinge 30, to facilitate emptying of the spoils tank. Further, in this embodiment, the vacuum unit 12, as illustrated schematically, is provided in a housing 32 which also houses a power pack 34 for powering the vacuum unit 12. In this embodiment the excavating/setting apparatus 1 further comprises a filter housing 36, for filtering air drawn by the vacuum unit 12 and a silencer 38 for mitigating noise made by the vacuum unit 12. Vacuum excavation, and apparatus for performing vacuum excavation is known per se, and the operation of the vacuum unit 12, spoils tank 14, power pack 34, filter housing 36, and silencer 38, will be understood and/or ascertainable by the skilled addressee. The operation of these parts, alone or in combination, will therefore not be described in detail herein. In this embodiment the vacuum unit 12, spoils tank 14, power pack 34, filter housing 36, and silencer 38 are mounted to a base frame 40, which is mounted to a chassis (not shown) of the truck 10. In this embodiment the excavating/setting apparatus 1 further comprises a lance 42 which can expel fluid under pressure to help break up material being excavated. The lance 42 is provided with a nozzle 43, through which fluid is expelled, and the nozzle may be selected from a choice of nozzles to assist in providing appropriate characteristics for a stream of fluid expelled therefrom. In this embodiment the lance expels pressurised fluid (e.g. primarily water). The excavating/setting apparatus 1 may further comprises a housing 44 which contains one or more water tanks and equipment (not shown) for pressurising the water and making it available to the lance 42. In one alternative, the housing 44 (and, if desired, a similar housing on the opposite lateral side of the spoils tank 14) may be used as a storage housing, for example for storage of 19 tools such as drills, saws and the like. In such an alternative the equipment (not shown) for pressurising the fluid (e.g. water) that is to be fed to the lance 42 may be provided in the housing 32 referred to above. Water for use by the lance 42 may be stored in a water storage tank (not shown) provided in any suitable location. In one embodiment water for use by the lance 42 is stored in a partitioned portion of the container that defines spoils tank 114, the partitioned portion being partitioned from the main volume of the spoils tank 14 so that such water is not contaminated by excavated material in the spoils tank 14. Such a partitioned portion of the container that defines spoils tank 14 would be provided with an outlet for egress of clean water, for example to the equipment (not shown) for pressurising the water and making it available to the lance 42. Additional or alternative storage containers (not shown) may also be provided on the vehicle as desired: for example, one or more storage containers may be provided beneath the deck of a truck, for example substantially below the spoils tank, and adjacent a chassis of the vehicle. Further, in this embodiment the truck 10 comprises a cab 46, which may be suitable for accommodating three or more people. In alternative embodiments the vehicle may be suitable for accommodating four, five, six, seven or more people. For example, the vehicle could comprise a truck having a cab with four doors and two rows of seats which may accommodate, and transport, up to seven people. Such seven seater trucks are known per se (and one example is the Hino 300 series 916 Dual Cab seven-seater). In this embodiment the excavating/setting apparatus 1 further comprises a number of legs 48, which may be arranged to engage the ground during operation to enhance stability. At least one leg 48A, and preferably at least one leg on each side of the apparatus 1, is directly associated with the crane 22. In this embodiment, the at least one leg 48A is connected to a base 52 of the crane 22. The at least one leg 48A may be connected to the base 52 of the crane 22 so that it can be moved horizontally (for example in a lateral direction of the vehicle) prior to downwards extension to engage the ground, in order to provide enhanced 20 lateral stability. The base 52 of the crane 22 may be connected directly to the chassis of the truck 10, for example by welding or by suitable fixings such as, for example, bolts. In this embodiment the truck has six ground engaging wheels or wheel sets 54, with more wheels towards the rear of the truck than towards the front. In this embodiment the four most rearward wheel sets each comprise two wheels, so that the truck 10 has eight wheels towards its rear and two wheels towards its front. It will be appreciated that other wheel arrangements are possible. For example the vehicle may provide two sets of wheels (for example associated with a single axle) at the rear thereof, and each set of wheels may comprise one, two or more wheels. Thus the vehicle may have two, four or more wheels towards its rear. Further, the vehicle may provide more than a single axle towards the front thereof. In one example the vehicle provides two axles towards the front thereof, each providing a steering capability: vehicles of this type are known per se and sometimes referred to as "twin steer" vehicles. The sets of wheels on the one, two or more axles provided towards the front of the vehicle may provide one, two or more wheels. Thus as alternatives to a vehicle providing a two wheels towards the front thereof the vehicle may provide four, six, eight or more wheels towards the front thereof. Further, one or more axles and associated sets of wheels may, if desired, be provided substantially at a longitudinal centre part of the vehicle. The truck 10 may comprise a hydraulic system which may have auxiliary circuits that provide quick release couplings in order to allow attachment of hydraulic tools. The truck 10 may comprise a pneumatic system which may have auxiliary circuits that provide quick release couplings in order to allow attachment of pneumatic tools. The truck 10 may be fitted with tool boxes for the storage of tools and equipment. Figures 2 to 5 illustrate an alternative embodiment of an excavating/setting apparatus, generally designated 100. The purpose of illustrating and describing this embodiment is to illustrate some variations and additions to the excavating/setting apparatus 1 of Figure 1. 21 Thus only the differences will be hereinafter described. It should be assumed that features of the excavating/setting apparatus 1 of Figure 1 can be included in the excavating/setting apparatus 100 of Figures 2 to 5. Elements and features of the excavating/setting apparatus 100 which correspond to elements and features of the excavating/setting apparatus 1 are designated by corresponding reference numerals but prefixed by the digit "1", and may not be introduced or described hereinafter. One difference between the excavating/setting apparatus 100 of Figures 2 to 5 and the excavating/setting apparatus 1 of Figure 1 is that the excavating/setting apparatus 100 provides at least one support, and in the illustrated embodiment first and second supports 160, 162, for supporting a particular type of object which is to be at least partially set into a cavity. In this embodiment the first and second supports 160, 162 are in the form of first and second cradles 164, 166, each mounted on stanchion 168, 170 which spaces the respective cradle above the deck of the truck 110. In this embodiment each cradle 164, 166 comprises a U-shaped member which provides a recess for receiving one or more poles 172 In this embodiment the first and second supports 160, 162 are adapted to support the one or more poles 172 so that the one or more poles may extend above the cab 146. This can allow poles of substantially the same length as the truck 110 to be supported, stored and transported. The one or more poles 172 may be secured in the cradles 164, 166 by securing elements such as suitable clamps, straps or the like (not shown). One difference between the excavating/setting apparatus 100 of Figures 2 to 5 and the excavating/setting apparatus 1 of Figure 1 is that the excavating/setting apparatus 100 provides a crane 122, which in a compact configuration, is arranged so that it extends in the length direction of the truck 110. This can assist in ensuring that the crane 122 is stored well clear of any poles 172 stored on the supports 160, 162, and can assist in operating the crane 122 from the compact configuration to a working (extended) state, without such operation being fouled by stored poles 172 (in other words, avoiding the operation causing the crane 122 to contact or impact the pole(s) 172. 22 Further, in the excavating/setting apparatus 100 of Figures 2 to 5 it will be appreciated that the inlet 116 of the spoils tank 114 is connected to an inlet conduit 126 which is supported by a boom arrangement 127. The boom arrangement 127 can assist supporting the weight of the conduit making movement and operation of the conduit easier and less strenuous. The outlet (not shown) of the spoils tank 114 can be located in any appropriate position, such as, for example, towards the front and top of the spoils tank 114. The spoils tank may, if desired, be provided with more than one inlet. For example in addition to the inlet 11 6of the top of the rear door 128. Figure 5 illustrates the excavating/setting apparatus 100, in use. As illustrated in Figure 5, the excavating/setting apparatus 100 is setting a pole 172 into a cavity 174. The crane 122 is provided with a pole holding arrangement 175, to enable movement of the pole 172 to be securely held and controlled. The connection of the crane 122 to the pole 172, including the pole holding arrangement 175, is illustrated schematically in Figure 6. As illustrated, the pole holding arrangement 175 comprises first and second jaws 176A, 176B which can be closed to retain a pole or opened to allow release of the pole 172. The crane provides a retractable wire rope 178, extendable from and retractable onto a spool 177. The spool 177 is mounted to the jib 126. The hook 125 of the crane 122 is attached to a distal end of the wire rope 178 and in use may be attached to a strap, chain or other lifting point 180 attached to the pole 172 at a lower part thereof. The jawsl 76A, 176B allow the pole to slide therethrough while retained, so the pole can be raised or lowered by the hook 125, even when the pole 172 is retained by the pole holding arrangement 175. Thus the hook 125 of the crane substantially supports the weight of the pole 172 at a lower part of the pole, and an intermediate part of the pole is retained in position relative to the jib 123 of the crane 122 by the jaws of the pole holding arrangement. This can greatly assist in avoiding uncontrolled movement of the top of the pole, which is important, because locations where poles are to be set into cavities may be in the vicinity of overhead power lines, and contact of the pole with such overhead power lines during 23 positioning of the pole is to be avoided. Of course, other means of retaining an intermediate portion of the pole close to the jib could be used if desired. If desired, alternative forms of pole holding device may be used. One such alterative comprises a set of jaws suitable for holding a pole. The set of jaws may be provided at the end of the crane arm to retain an intermediate part of the pole relative to the end of the crane arm. The power required to operate the crane may be supplied from any desired source, but it is convenient to use a source provided by or on the vehicle such as a power take off (PTO) unit fitted to the truck, a livedrive unit fitted to the truck, or an auxiliary engine (such as a petrol or diesel engine) which may be provided as the power pack 34 provided in the housing 32 referred to above. Similarly the power to operate the vacuum unit 12, 112, may be provided by a power take off (PTO) unit fitted to the truck or a livedrive unit fitted to the truck, rather than by the power pack 34. Power may be made available from two or more of these options (or some other power source) to provide operator choice and or redundancy. In an embodiment the same power source, associated with the vehicle (for example a PTO unit fitted to the vehicle, a livedrive unit fitted to the vehicle, or an auxiliary engine mounted on the vehicle) is used as a power source for both the crane and the vacuum unit. This can provide efficiency and convenience and consequent cost and time savings, as it can reduce the need to turn on and off engines. For added convenience, the vehicle may provide an auxiliary ignition switch, outside of the cab, for allowing the vehicle engine to be turned on and off. Provision of an auxiliary ignition switch may be particularly appropriate where a livedrive is used since power may be provided from a vehicle engine via a livedrive independent of the (transmission) gear state of the vehicle. An interlock may be incorporated so that the vehicle engine can only be started using the auxiliary ignition switch when the vehicle is in neutral gear and/or when the parking brake is applied. 24 The crane 22, 122 and the vacuum pack 12 may have user operable controls (for example levers, switches and the like provided on the vehicle. In an embodiment the controls for the crane 22, 122 and the vacuum pack 12 are provided close to each other, or in an integrated control panel, mounted on the outside of the vehicle (for example, close to the crane or the vacuum pack). Alternatively or additionally, the crane 22, 122 and the vacuum pack 12 may be controllable by wireless or wired remote control. In an embodiment a single remote control unit is provided which can be used to operate both the crane 22, 122 and the vacuum pack 12, and may thus be regarded as a combined remote control. The combined remote control unit may be wireless, and may be switchable between a first mode in which it allows a user to control the crane 22, 122 and a second mode in which it allows a user to control the vacuum pack 12. An auxiliary ignition switch may be provided with or adjacent the other controls, for example mounted on the outside of the vehicle and/or on a remote control unit. (Auxiliary ignition switches, including vehicle mounted and wireless remote control auxiliary ignition switches, are known per se, and will not be described in detail herein.) The crane, in each of the described embodiments, 1, 100, may be hydraulically powered, may be operated by extension and retraction of cables (for example wire ropes), or may be operated by a combination of hydraulics and cables. An example of a crane 122 is illustrated schematically in Figures 7(a) which shows a compact configuration and Figure 7(b) which shows a working or extended configuration. In the illustrated embodiment the crane 122 comprises a base 152 (which can be mounted to the truck 10, 110) and which provides extensible ground engaging legs 148A, a first elongate member 182 connected to and articulated relative to the base 152, a second or intermediate elongate member 184 connected to and articulated relative to the first elongate member 182, and a third elongate member or jib 123, connected to and articulated relative to the second elongate member 184. The jib 123 may have telescoping sections. The crane is operable by hydraulic rams 186, 188. 25 The crane illustrated the commercially available HIAB TM XS 099 loader crane, although of course other types and models of crane could be used. For example, in alternative embodiments PALFINGER T M 8500 Series, 9000 Series or 10000 Series cranes might be used. In further alternative embodiments, cranes suitable for higher loads and/or longer reach (for example, but not limited to, PALFINGER T M 36000 Series, 40000 Series, 48000 Series, or other similar capacity cranes) or cranes suitable for smaller loads and/or shorter reach (for example, but not limited to PALFINGER T M 4200 Series, 4500 Series, 5000 Series, or other similar capacity cranes) could be used, depending on the load capacity and reach required. Of course, other types crane, and other options for operating the crane should not be considered to fall outside the scope of the present disclosure: for example, it may be practicable to use a pneumatically operated crane. In the case of a crane that is at least partially pneumatically operated, a pneumatic system of the vehicle (for example the truck 10, 110) may be utilised. Further, as an alternative (or additional) to use of a hook arrangement for lifting the object (for example a pole as illustrated in Figure 6), the lifting and setting apparatus (which may be a crane) may comprise a grapple suitable for engaging, lifting and manipulating the object. Grapples, for use as attachments to cranes are known per se and commercially available. Where the object is a pole, a pole grapple which is capable of exerting the amount of torque to a pole to effect the desired control, orientation and manipulation may be used. One example of a grapple that may be suitable for lifting and setting at least some types of pole is a Kinshofer KM 930 grapple. In an alternative embodiment, the lifting and setting apparatus may be an apparatus which is not a commercially available crane, but which can nonetheless effectively lift and move the object which is to be set into the cavity. For example, a robotic arm arrangement with suitable size and strength could be used. By way of example, robotic arms are sometimes 26 used in the minerals drilling industry for transferring drill rods from a rod holder to a drilling rig (where the drill rod can be connected to other drill rods to form part of a drill string). One commercially available product along these lines is the 'Bionic arm' Model 030703A pipe handler developed and marketed by Maxidrill Inc. (a Canadian company). However, vehicle mounted cranes, such as, for example the Hiab XS 099, are readily available and are currently considered to be a more economical option, as well as having controls which will be more familiar to, and/or easier to master by, likely operators of the excavating/setting apparatus described herein. As illustrated in Figure 5, the pole 172 is supported by the crane 122 in a substantially vertical orientation, is move to a position substantially above the cavity 174 in which it is to be set, and is then lowered into the cavity. The cavity 174 is a cavity which has been previously excavated by moving material from the location where the cavity is desired into the spoils tank 114, under suction provided by the vacuum unit 112. More broadly, the excavating/setting apparatus 100 of Figures 2 to 5 and the excavating/setting apparatus 1 of Figure 1 can be used in the following manner. The apparatus is loaded with one or more objects to be set into a cavity and, if desired, with additional equipment that might be needed, for example one or more of: a drill, a saw, a tamper, a pole jack, an auger, a pole grab, a ladder, a pole platform, etc. The apparatus 1, 100 is driven to the location where it is desired to excavate a cavity and set an object at least partially within the cavity. The driving operation can be performed by a single person. The cab 46, 146 may accommodate two or more people, which may be sufficient for the operations to be performed, so that only a single vehicle need be taken to the working site. As foreshadowed above, the vehicle may be provided in a form that can accommodate a larger crew, for example a crew of seven, so that even if a relatively large crew is required on-site, all crew required can be transported in a single vehicle, so that only a single vehicle need be taken to the working site. If desired, since only one person is 27 required to transport all the required equipment, and the objects, to the working site, others workers (if any) may arrive without the need to bring equipment. This can allow all workers at the site except one to arrive from any location, whether or not they have equipment with them, and free them from the need to travel to a location where equipment is stored prior to arrival at the site. This means that they may, for example, travel to the working site direct from their homes, and by public transport or domestic vehicle, rather than having to travel via a location where equipment is stored and travel to the working site in a vehicle suitable for transporting equipment to the site. Further, there are circumstances under which only a single worker is required to perform the excavation and setting operations. An example is erection of a "property pole", which is a pole on private property which will subsequently be used to support a transmission cable, such as a telecommunications cable or a power cable. One or more property poles are often erected in advance of provision of the cable, and in a location where, at the time of erection, there are no powered overhead cables, thus making one-man installation more appropriate than when poles are to be erected in the vicinity of powered overhead cables (under which circumstances it is normally appropriate, for safety reasons, to have at least two workers present). Another example of circumstances under which only a single worker is adequate perform the excavation and setting operations is in the excavation of cavities for fence posts, and the setting of fence posts therein. When the apparatus 1, 100 is at the desired location a cavity is excavated in the ground. This will typically be done by breaking up material forming the ground using a lance (e.g. lance 42 and an appropriately selected nozzle) and by moving the material, under suction provided by the vacuum unit (e.g. vacuum unit 12, 112), through a conduit (e.g. inlet conduit 26) into a spoils tank (e.g. spoils tank 14, 114). If the material to be excavated is too hard (e.g. rock or shale) or otherwise unsuitable for excavation as described above, a drill or auger operated via the lifting and setting apparatus (for example a hydraulically driven auger attached to the crane 22, 122) may be used to at least assist in excavating the desired 28 cavity. Augers for use as attachments to cranes are commercially available: such augers, and operation of such augers, are known per se and will not be described in detail herein. In this case it may be appropriate for the operator to check in advance that there are no assets in the ground that might be damaged by such mechanical excavation. The crane 22, 122 (or other lifting and setting apparatus) is then used to lift the object to be set into the cavity, move the object to an appropriate position above the cavity, and set the object at least partially into the cavity by lowering the object. If, at this stage, it is found that the cavity is insufficiently large or deep for desired setting of the object, the object may be raised out of the cavity (using the crane or other lifting and setting apparatus) moved to be clear of the cavity, and further excavation may be performed. Notably, because the crane and the vacuum-unit/spoils-tank arrangement are mounted on one vehicle, this does not require movement of a vehicle carrying one of these types of equipment away from the cavity to allow the other type of equipment to be brought close to the cavity, even in the circumstances where space near the cavity is restricted so that only one vehicle can be positioned adjacent the cavity. It is especially desirable to have the vacuum-unit/spoils-tank arrangement close to the cavity when a boom is being used, as booms have limited range. Further, a single user may conveniently control the operation of both the crane and the vacuum-unit/spoils-tank arrangement from the vehicle, without having to move between different pieces of apparatus or different vehicles on which different pieces of apparatus are mounted. If a combined remote control unit is provided a single user may control the operation of both the crane and the vacuum-unit/spoils-tank arrangement using the combined remote control. When the object is set in the cavity its position can be adjusted if desired, for example by tamping and the object can be secured in the cavity, for example by back filling, pinning, application of cement, or any combination thereof. 29 Although a pole 172 is illustrated in Figures 2 to 6, it will be appreciated that the present disclosure also applies to the excavation of cavities for other objects, and to the setting of such other objects at least partially within a cavity. For example, a cavity can be excavated in which a pit is set. In another example a cavity can be excavated in which a valve (such as a large valve for connection with underground pipework, such as of a water main) is set. In a further example a cavity in the form of a trench can be excavated in which a pipe or a section of pipe is at least partially set. In a further example a cavity can be excavated in which a foundation (such as, but not limited to, a precast concrete foundation) is set. Use of such foundations can provide an alternative way of erecting poles to setting the poles into the ground: for example, a foundation (such as, but not limited to, a precast concrete foundation) can be set at least partially within an excavated cavity, and a pole secured to the foundation, for example by bolting a flange provided at the bottom of the pole to the foundation. The described apparatus is also of utility for replacing a damaged or decayed object. Figures 8(a) to 8(j) illustrate schematically sequential stages in an embodiment of a replacement method. In this embodiment a damaged or decayed pole 173 is to be replaced with a new pole 172. As illustrated in Figure 8(a), when the apparatus is at the desired location (in this example the location where the damaged or decayed pole 173 is located) the new pole 172 is unloaded from vehicle, and in this example unloaded from cradles 164, 166, using the lifting and setting apparatus, in this example embodied by the crane 122. In this example a sole worker 190 operates the crane 122 by use of a wired remote control 192 which is connected to the rest of the apparatus by a cable 194. As illustrated in Figure 8(b), after the new pole 172 is set down (in this example on the ground) a pole jack 196 is set up, attached to the damaged or decayed pole 173. 30 As illustrated in Figure 8(c), the damaged or decayed pole 173 is engaged by the crane 122, and specifically by the pole holding arrangement 175. As illustrated in Figure 8(d), material around the base of the damaged or decayed pole 173 is then excavated to loosen the damaged or decayed pole 173. As illustrated in Figure 8(d), a lance (for example lance 42 with an appropriate nozzle 43) is used to loosen material around the base of the damaged or decayed pole 173. The inlet conduit 126 (not shown in Figure 8(d)) is also used to pass the material into the spoils chamber 114 of the apparatus 100. Thus a space or cavity 198 is partially excavated, which at this stage extends around the base of the damaged or decayed pole 173, and which will normally, at this stage, be shallower than the depth by which the damaged or decayed pole 173 is set into the ground. As illustrated in Figure 8(e), the pole jack 196 is used to remove the damaged or decayed pole 173 from the ground. The damaged or decayed pole 173 is stabilised by the crane 122 during removal. The crane 122 may also provide some upwards force to assist removal of the damaged or decayed pole 173. The pole jack 196 is used because the upwards force that can be applied by the crane is (at least in this example) insufficient, on its own, to effect removal of the damaged or decayed pole 173. If the upwards force that can be applied by the crane is sufficient, on its own, to effect removal of the damaged or decayed pole 173 (as may be the case in some circumstances) the pole jack 196 need not be used. As illustrated in Figure 8(f), the damaged or decayed pole 173 is lifted and set on the cradles 164, 166 by use of the crane 122, for transportation away from the working site. As illustrated in Figure 8(g), the cavity 198 is then enlarged, ready for receipt of the new pole 172. Again, this can be achieved by use of a lance (not shown in Figure 8(d)) with an appropriate nozzle to loosen material, and use of the inlet conduit 126 to pass the material into the spoils chamber 114. 31 As illustrated in Figure 8(h), backfill material 200 is then unloaded from the vehicle 110 (on which it was transported to the working location) by the worker 190, using the crane 122. The backfill material 200 is placed close to the cavity 198 to facilitate insertion into the cavity 198, as will be described in due course. As illustrated in Figure 8(i), the crane 122 is used to move the new pole 172 and set it in the cavity 198. As illustrated in Figure 8(j), the cavity around the new pole 172 is then backfilled using the backfill material 200, and the backfill material is compacted, in this example using a tamper 202 or compactor. The tamper 202 or compactor may be hydraulically or pneumatically driven, and may be connected to an auxiliary hydraulic or pneumatic outlet of the vehicle (not shown in in Figure 8(j)) by a hydraulic or pneumatic hose 204. At this stage the new pole 172 will typically remain supported in its desired (typically substantially vertical orientation) by the crane 122 and pole holding arrangement 175. When the backfilling operation is completed and the new pole 172 is securely positioned the crane 122 and pole holding arrangement 175 can be disconnected from the new pole 172, and the replacement operation is complete. The poles 172 and 173 may be poles used to support overground distribution cables, for example power or telecommunications (including telephone) cables. In this case such cables would be removed from the damaged or decayed pole 173 prior to its removal, and attached to the new pole 172 using suitable cable supports which are known per se, after the replacement operation. In a variation of the above replacement method, the new pole may be erected prior to removal of the pole to be replaced. In this variation a cavity for the new pole is excavated close to the pole to be replaced, and the new pole is set in the cavity. After erection of the new pole is complete, one or more cables (for example distribution cables such as power or telecommunications transmission cables) may be detached from the pole to be replaced and 32 attached to the new pole prior to removal of the pole to be replaced. This can avoid problems associated with unsupported portions of cable which could occur if the pole to be replaced is removed prior to erection of the new pole. It will be appreciated that such problems (if any) may be addressed by other means if the pole to be replaced is removed prior to erection of the new pole (as illustrated in Figures 8(c) to 8(i)), for example a temporary support for the cable portion(s) may be used. Of course, the apparatus 1, 100 can be used to provide new poles where no poles previously existed. In this case the operations described above with reference to Figures 8(b) to 8(f) would not be required. Thus it will be appreciated that embodiments of apparatus described herein are well suited to setting up a line of poles for supporting cables of a distribution system. It will be appreciated from the above that the arrangements and methods described herein can provide substantial benefits in both transportation and operation compared to using two or more different vehicles to transport and/or position the chamber (e.g. spoils tank 14, 114) and a lifting and setting apparatus (e.g. crane 22, 122). Many modifications to, and variations of, the described embodiments are possible. For example, the illustrated embodiments provide the chamber (e.g. spoils tank 14, 114) closer to the rear of the vehicle than is the lifting and setting apparatus. This is convenient for a chamber which has a rear door, and which can be tipped longitudinally to facilitate emptying. In an alternative embodiment the chamber (e.g. spoils tank 14, 114) may be provided closer to the front of the vehicle than is the lifting and setting apparatus. This may be appropriate if it is desired to have the lifting and setting apparatus provided at or towards the rear of the vehicle, and may be convenient for a chamber which has a side or lateral door, and which can be tipped laterally to facilitate emptying. In either case a storage region may be provided at some region between the chamber and the lifting and setting apparatus. 33 Further, the illustrated embodiments describe the vehicle as being a truck, but other vehicles could be used, for example a trailer or a suitable boat (which may be of particular use for locations such as river banks, which may be easily accessible by boat but difficult to access using a heavy road-going vehicle). Modifications and improvements may be incorporated without departing from the scope of the disclosure herein and the appended claims. 34