Now I've looked over my wiring and I can't see anything wrong with it (which is a good thing I suppose), but the hum was still there. I took it to an electrical engineer friend of mine, who happens to be a much better guitarist than me, but I digress.
He also couldn't fault my wiring, and said that the problem lay in that the pot was working too well and creating a link between the hot and ground (which I thought was supposed to happen) and it was this that was causing the noise??? He reckoned that normally, pots don't drain all signal to ground and therefore you don't get this noise?
He 'solved' the problem for me (and I say 'solved' because I'm not convinced it's the right way to do it) but putting a tiny resistor in series with the hot lead from the jack socket, before it reaches the volume pot. It is high enough to kill the hum I get, but apparently it is low enough to not interfere with the signal.
I don't think this is right at all and at best seems like a bodge job to me.
Is my wiring right and should all guitars do this??? help!!!!