ISOLATING STOP COCK VALVE Field of the Invention The invention relates to isolating stop cock valves and their use to isolate mains water 5 supplies from appliances normally receiving water through the stop cock valves. Background of the Invention Isolating stop cock valves are used to enable disconnection of downstream appliances, such as toilet cisterns, washing machines, dishwashers, mixer taps, by isolating the mains water supply normally connected through the stop cock valve and in use supplying water to the .0 attached appliance(s). A common isolating stop cock valve device which has been used in the plumbing industry for many years has a valve body having a female threaded inlet. To seal the inlet with the female thread to a supply having a male threaded nipple, a trades person or handy man must use a sealing compound such as Teflon tape, hemp or the like. One disadvantage with this type of seal .5 is that, when not enough Teflon tape, hemp or the like is used, it leaks. Another disadvantage is when too much Teflon tape, hemp or the like is used, the female inlet end of the stop cock can easily split rendering the stop cock useless. A further disadvantage with this type of seal is that it is difficult to control the sealing tightness under varying water pressure and to align the stop cock to the appliances. -0 Objects of the Invention It is an object of the present invention to provide a plumbing isolating stop cock valve which can overcome or substantially ameliorate at least one of the disadvantages of the prior known stop cock valves outlined above. 25 It is a further and preferred object of the present invention to provide a plumbing isolating stop cock valve which is to be connected to conventional fittings including the conventional water supply fitting provided with a male externally threaded supply nipple. It is an object of the present invention in a second aspect to provide a method of plumbing an appliance or fitting so as to be connected to a mains water supply having a male externally 30 screw threaded nipple and so as to enable selective supply of water to the appliance or fitting or 1 isolation of the appliance or fitting from the mains water supply wherein the method can overcome or substantially ameliorate at least one of the disadvantages of the use of prior known stop cock valves outlined above. Summary of the Invention 5 According to a first aspect of the present innovation there is provided a plumbing stop cock valve to be installed between a mains water supply comprising a male externally screw threaded nipple and a downstream appliance or fitting so as to enable isolation of the mains water supply and disconnection of the downstream appliance or fitting, the stop cock valve including: a body having an inlet, an outlet out of which water is supplied to the appliance or fitting, [O and a water flow passage through the body connecting the inlet to the outlet, a valve seat associated with the flow passage, a valve closure member movable between a closed position in which it engages the valve seat to close the flow passage and an open position in which it is lifted from the valve seat to open the flow passage, and L5 operating means connected to the valve closure member for selectively moving the valve closure member between its closed and open positions, wherein the inlet of the body has operatively associated therewith a female internally threaded swivel nut which engages with the externally screw threaded nipple to install the stop cock valve for 20 selectively passing water therethrough to the appliance or fitting or closing the flow passage to isolate the appliance or fitting, and a sealing insert is provided in the swivel nut of the inlet and which forms a seal between the male externally screw threaded nipple of the mains water supply and the body. In one possible embodiment, the sealing insert comprises a sealing grommet inserted within 25 the swivel nut and which sealingly engages with the supply while allowing flow from the supply into the inlet of the flow passage in the body. The sealing insert may have a conical shape facing towards and engageable with the supply. 2 The sealing insert may be composed of a rubber material. Alternatively, the sealing insert may he composed of a fibre material and forms a fibre gasket for sealing engagement with the supply when the swivel nut is engaged with and tightened onto the externally screw threaded male portion of the supply. 5 According to a second aspect of the present innovation there is provided a method of plumbing an appliance or fitting so as to be connected to a mains water supply having a male externally screw threaded nipple and so as to enable selective supply of water to the appliance or fitting or isolation of the appliance or fitting from the mains water supply, the method including the steps of: .o . providing a plumbing stop cock valve which includes: a body having an inlet, an outlet out of which water is supplied to the appliance or fitting, and a water flow passage through the body connecting the inlet to the outlet, a valve seat associated with the flow passage, a valve closure member movable between a closed position in which it engages the valve .5 seat to close the flow passage and an open position in which it is lifted from the valve seat to open the flow passage, and operating means connected to the valve closure member for selectively moving the valve closure member between its closed and open positions, wherein 20 the inlet of the body has operatively associated therewith a female internally threaded swivel nut, and a sealing insert is provided in the swivel nut of the inlet, " installing the stop cock valve by engaging the internally threaded swivel nut with the 25 externally screw threaded nipple and tightening the swivel nut until the sealing insert forms a seal between the nipple of the mains water supply and the body of the valve, * connecting the appliance or fitting to the outlet of the valve, and 3 e selectively operating the operating means of the valve either to connect mains water to the appliance or fitting, or to isolate the mains water enabling disconnection of the appliance or fitting. Short Description of the Drawings 5 An embodiment of the invention is described in detail in the following passages of the specification which refer to the accompanying drawings. The drawings, however, are merely illustrative of how the invention might be put into effect, so that the specific form and arrangement of the various features as shown is not to be understood as limiting on the inventions. In the drawings: .0 Figure 1 is a cross-sectional view of an isolating stop cock valve of a conventional known construction and operation. Figure 2 is cross-sectional view of an isolating stop cock valve according to a first possible embodiment of the present invention, and Figure 3 is a cross-sectional view of an isolating stop cock valve according to a second .5 possible embodiment of the present invention. Detailed Description of the Drawings In the known type of isolating stop cock valve illustrated in Figure 1, the valve I has the valve body 2 having an inlet 4 and an outlet 5 with a flow passage 3 passing from the inlet 4 to the outlet 5. A valve seat 6 is located within the body 2 surrounding the passage 3 intermediate 20 the inlet 4 and the outlet 5. A valve closure member 7 is selectively operable by operating means shown as including the rotatable tap handle 8 to move the valve closure member 7 from its open position lifted from the valve seat 6 enabling flow through the passage 3 (as illustrated in Figure 1) and a closed position (not shown) in which the valve closure member 7 engages with the valve seat 6 to close the passage 3 and thereby isolate the outlet 5 from the inlet 4. 25 The inlet 4 of the valve body 2 in the known stop cock valve of Figure 1 has an internally threaded female portion indicated by the reference numeral 12. In use, this female internally threaded inlet 4 is screwed onto a male externally threaded supply nipple (not shown). This involves rotating the entire valve body 2 to mount the isolating stop cock valve onto the supply nipple. 4 In the embodiment of the present invention illustrated in Figure 2, the inlet 4 has a swivel nut 11 having the female internally threaded section 12 for screw threaded engagement with an externally screw threaded supply nipple. By providing the swivel nut I1 used to mount the stop cock valve 1 to the supply, the requirement to rotate the entire valve body 2 (which is required 5 with the valve of Figure 1) is eliminated. The embodiment of Figure 2 includes a sealing insert 10 inserted within the swivel nut 11 arranged so that the sealing insert 10 forms a seal with the supply having the externally screw threaded nipple with which the internal screw thread 12 of the swivel nut I1 is engaged. The sealing insert 10 is illustrated in the form of a grommet providing for water flow from the inlet 4, [0 through the grommet, then through flow passage 3 and the valve seat 6 and then to the outlet 5. The grommet 10 is shown having a conical shape facing outwardly from the inlet 4 so as to engage with and seal to the supply. The conical grommet may be composed of a rubber material. In the second embodiment of Figure 3, instead of the rubber cone grommet 10 of Figure 2, there is provided a fibre gasket 13 inserted in the swivel nut 11 and positioned so that the gasket .5 13 sealingly engages with the externally screw-threaded supply received within and engaging with the internal screw thread 12 of the swivel nut 11. In the embodiments of Figures 2 and 3, the axis 9 of the outlet 5 is perpendicular to the axis of the inlet 4 and valve closure member 7. However the axis 9 of the outlet 5 may be at different angles to the axis of the inlet depending on requirements. 10 It will be seen that the embodiments of the isolating stop cock valve according to the invention illustrated and described herein have a different configuration and construction to the known stop cock valve shown in Figure 1. This different configuration enables the valve to be easily mounted to a male threaded supply nipple and provides effective sealing to prevent leakage in a simpler manner than the use of Teflon tape or hemp packing or the like used in the 25 past with the Figure 1 valve. The swivel nut in the embodiments of the invention enables the valve to be connected to conventional fittings, namely the conventional male externally threaded water supply nipple. The isolating stop cock valve of the present invention can be used with a water supply line which, in use, supplies water through the isolating stop cock valve to downstream appliances 30 such as a toilet cistern, washing machine, dishwasher, a mixer tap. 5 It is to be understood that various alterations, modifications and/or additions may be made to the features of the possible and preferred embodiment(s) of the invention as herein described without departing from the spirit and scope of the invention. 5 6