THE INVENTION The invention relates to a ground anchor and installation method. BACKGROUND OF INVENTION Ground anchors are widely used to retain, brace and secure an item or structure in a desired position either in or above the ground, for example such as retaining and securing a post, typically a post or support member, in an upright position. A problem with posts or support members, is that they can be pulled over, become loose or come out of the ground such as when load is applied by tensioned wires or by load created by crops growing on trellising being supported by the posts or stock leaning and rubbing against the post. Either way the post and fence or trellis integrity and usefulness can be severely compromised. Other known methods of bracing posts is to create a diagonal support stay or brace member that is positioned against the main post member, such that it will become under compression, resisting the forces created by the tensioned wires or trellising. Whilst this method is generally effective as a stay support, it does consume space on the tensioned side of the main post member, whereas this space could otherwise be used for production with growing crops such as grape vines in the viticulture industry. Alternatively there are a number of existing methods utilized to provide means of creating ground anchor points, existing methods include burying a member, screwing or rammed anchors. However there are inherent problems with installation of existing anchors into rocky ground conditions. Burying a member to create an anchor attachment is typically expensive as it involves significant time and effort to firstly excavate a hole then bury an anchor and compact the retaining earth material. Buried anchors are generally unable to withstand full load until sometime after installation due to a required period of settling and natural compaction. Screw anchors are relatively easy to install however they can only be installed in relatively soft earth as they are limited by rocky ground conditions. Existing driven anchors systems can be installed by conventional means i.e. post drivers, vibrating compactors or manual drivers for small anchors. A driving tool is inserted into a receptive hole or cavity in the 1 anchor to enable the anchor to be driven into the earth, edge first. Once driven to the required depth the driving tool is removed, a lifting force is applied to the attached line or tie rod to set the anchor, forcing it to skew across the hole and resist extraction from the ground. Existing driven anchors suffer inherent limitations, as the design incorporates the driving tool being inserted into the receptive means in the anchor, the anchor is therefore in contact with the ground as it is forced ahead of the driving tool. As such existing driven anchors are not able to withstand being driven into rocky ground conditions. To overcome this limitation a pre-spiked hole is created by driving a rock breaking shaft into the earth prior to installation of the anchor. The necessity to pre-spike the hole adds significant cost to the installation and still suffers installation problems when rocks inevitably fall into the spiked hole ahead of the anchor. Whilst the current known methods go some way in achieving the result they do have disadvantages such as being labour intensive, time consuming, not suitable for all type of ground conditions and ease of use. DEFINITIONS It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process. OBJECT OF THE INVENTION It is an object of the invention to provide a ground anchor that ameliorates some of the disadvantages and limitations of the known art or at least provide the public with a useful choice. 2 SUMMARY OF INVENTION In a first aspect the invention resides in a ground anchor including: a) a hollow tubular body adapted to accommodate a spigot portion of a drive tool such that the spigot portion is adapted to sit flush with or slightly protrudes through and open end the hollow tubular body; b) an attachment means situated on the hollow tubular body such that the longitudinal axis of attachment means is offset to the central longitudinal axis of the hollow tubular body; c) an elongate means pivotally connected to a connecting means on the attachment means; wherein upon insertion of the ground anchor into the ground by the drive tool a pulling force applied to the elongate means causes the hollow tubular body, due to the offset positioning of the attachments means relative to the central longitudinal axis of the hollow tubular portion, to pivot and transversely cross lock across the preformed hole in order to resist and prevent the hollow tubular body portion and hence the ground anchor from being removed from the ground. In a second aspect the invention resides in a driven anchor system for driving and securing a ground anchor in the ground; the drive system includes: a) the ground anchor of the first aspect; b) a drive tool having an elongate shaft having a ground engaging spigot at one end and a head portion at the other end to assist in driving the ground anchor in to the ground; wherein the hollow tubular body portion of the ground anchor is adapted to accept the spigot of the drive tool such that the spigot sits flush with or slightly protrudes through and open end the hollow tubular body so that the spigot is in direct contact with the ground as the ground anchor is being inserted in to the ground by the drive tool, and upon removal of the drive tool after insertion of the ground anchor the hollow tubular body is adapted due to the offset positioning of the attachments means relative to the central longitudinal axis of the hollow tubular portion to pivot and transversely cross lock across the preformed hole upon a pulling 3 force being applied to the elongate means so that the hollow tubular body portion and hence the ground anchor are able to resist being removed or lifted out of the ground. Preferably, the tubular body portion has protrusions extending longitudinally along the anchor body to further improve the resistance of the ground anchor from being removed or lifted out of the ground. Preferably, the protrusions are winged flutes that extend in a longitudinal plane that is substantially 900 to the longitudinal plane of the attachment means. Preferably, the drive tool is made from steel. Preferably, the spigot is tapered to assist the insertion and subsequent extraction of the spigot from the hollow tubular portion. Preferably, the elongate means is a tie rod or flexible tie pivotally connectable at one end to the attachment means, the other end of the tie rod or flexible tie when the ground anchor is inserted in to the ground, preferably extends above the ground surface so as to allow a pulling force to be applied to the ground anchor in order to cause the hollow tubular portion to pivot and transversely cross lock across the preformed hole and to allow the tie rod or flexible tie to be attached to the item or structure being anchored by the ground anchor. Preferably, the attachment means is a flange or web that extends transversely outwardly from the hollow tubular body. Preferably, the connection means is an aperture in the attachment means such that an end portion of the tie rod or flexible tie is pivotally connected to the attachment means via the aperture. Preferably, the connection means is a pivot pin, clasp, eyelet or clamp fixed to the attachment means such that an end portion of the tie rod or flexible tie is pivotally connected to the attachment means via the clasp, eyelet or clamp. Preferably, the tie rod is galvanised steel rod or wire. Preferably, the ground anchor as claimed in any one of the preceding claim, wherein the hollow tubular body is made from metal, steel, plastic, fibre glass, wood or any composite thereof. 4 Any other aspects herein described BRIEF DESCRIPTION The invention will now be described, by way of example only, by reference to the accompanying drawings: Figure 1 shows a perspective view of a ground anchor in accordance with a first preferred embodiment of the invention. Figure 2 shows a close up perspective view of the ground engaging part of the ground anchor as shown in figure 1. Figure 3 shows a side view of the installation drive tool for inserting the ground anchor into the ground. Figure 4 shows a side view of the ground anchor shown in figure 1 being inserted into the ground by the installation drive tool shown in figure 3. Figure 5 shows the installation drive tool being extracted following installation of the ground anchor. Figure 6 shows skew action of the ground engaging part when a lifting force is applied to the ground anchor. Figure 7 shows a perspective view of a ground anchor with wings in accordance with a second preferred embodiment of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENT(S) The following description will describe the invention in relation to preferred embodiments of the invention, namely a ground anchor. The invention is in no way limited to these preferred embodiments as they are purely to exemplify the invention only and that possible variations 5 and modifications would be readily apparent without departing from the scope of the invention. The invention resides in a ground anchor, typically a driven ground anchor, providing efficient, effective, reliable installation and load holding properties for many different applications. A key feature of the invention is that the driver shaft not only guides the ground anchor but also engages directly with the ground, enabling it to function as a rock breaker, achieving installation in a single operation without the requirement for a separate rock breaker pre-spike or excavation operation. Figures 1 and 2 shows a ground anchor G having a tubular body portion 1 having a hollow section 2 there through. A flange 3 extends outwardly from the tubular body portion 1 and tie rod 4 is pivotally connected to the flange 3. The flange 3 is positioned on the hollow tubular body 1 such that the longitudinal axis of flange is offset to the central longitudinal axis of the hollow tubular body 1. The tie rod 4 is pivotal connected to flange 3 through an aperture in the flange 3, however other forms pivot connections could be envisaged such as pivotally connecting the tie rod to a pivot pin, clasp, eyelet or clamp that are attached to the flange. The tie rod could be replaced by a flexible tie, such as rope, tape, etc. Figure 3 shows a front elevation of the installation drive tool D having a shaft 5 with spigot 6 and shoulder 7 at one end and shaft head 8 at the other end. The spigot 6 is tapered from the shoulder 7 and the distance from the shoulder 7 to the free end of the spigot 6 is equal or slightly longer than the length of the hollow tubular body 1 such that when ground anchor is being driven into the ground the free end of the spigot sits flush with or slightly protrudes through an open end the hollow tubular body 1 (figure 4) so that the spigot 6 is in direct contact with the ground as the ground anchor G is being inserted in to the ground by the drive tool thus enabling the spigot to engage and subsequently break through hard ground and/or rocks that are in the path of the ground anchor being driven into the ground. In Figure 4 the ground anchor G is shown with installation drive tool D being inserted below ground level 9. Figure 5 shows the installation drive tool D being extracted following installation of the ground anchor G below ground level. A portion the tie rod remains above ground level 9 such that upon application of a pulling force 10 (Figure 6) the hollow body portion, due to the offset positioning of the flange 3 relative to the central longitudinal axis of the hollow tubular portion, pivots and transversely cross locks across the preformed hole in 6 order to resist and prevent the hollow tubular body portion 1 and hence the ground anchor G from being removed the ground. Once the ground anchor G is anchored in place the above ground end of the tie rod 4 can be secured to the item or structure being anchored. Figure 7 shows an alternative ground anchor G where the hollow body portion 1 has winged flutes 11 that extend outwardly from the hollow tubular body and positioned in a longitudinal plane that is substantially 900 to the longitudinal plane of the flange 3. ADVANTAGES a) Easy to use b) Installation is achieved with a single process as compared to existing designs requiring a pre-spike operation when installing in rocky ground conditions c) Can be installed using a conventional mechanical post driving machine. d) Able to be used in all soil or ground types e) Is installed on the side of the post member, opposite to the trellis or tensioned wires enabling full unencumbered crop production to extend right up to the post member EQUIVALENTS CLAUSE. The Invention may also broadly be said to consist in the parts, elements and features referred or indicated in the specification, individually or collectively, and any or all combinations of any of two or more parts, elements, members or features and where specific integers are mentioned herein which have known equivalents such equivalents are deemed to be incorporated herein as if individually set forth. The examples and the particular proportions set forth are intended to be illustrative only and are thus non-limiting. VARIATIONS The invention has been described with particular reference to certain embodiments thereof. It will be understood that various modifications can be made to the above-mentioned 7 embodiment without departing from the ambit of the invention. The skilled reader will also understand the concept of what is meant by purposive construction. KIT OF PARTS It will also be understood that where a product, method or process as herein described or claimed and that is sold incomplete, as individual components or steps, or as a "Kit of Parts", that such exploitation will fall within the ambit of this invention even though there may not be any claim to a kit of parts included in the following claims. 8