Thank you very much PLOD, the keyswitch arrived in the post today - I will send you money to cover the postage and a pint for you mate
Fitting it was quite simple, the only thing that 'annoyed' me were the two different nut sizes inside the control box - one was an 8mm & the other was a 9/32. I undid the 8mm and then proceeded to undo the second one and after about 20 mins. of failing to turn the nut with an 8mm socket I tried a different size.
Just need to fabricate the bracket to hold the second keyswitch when it's not in use.
Pictures;