gstuart, I've been a bit busy and only just seen your latest post so apologies for not replying until now.
Anyway, I got the new (second hand) switch, fitted it,still no fogs! Not quite at hair pulling stage yet so checked through everything again. Tested the new switch just incase, pulled fuses out, put fuses back etc etc. Tested power to switch and found nothing! Now I'm head scratching! Check everything again, tried finding these connectors behind the headlights with not much luck so unfortunately cannot tell you what voltage I have at them. After a bit bit more checking and wiggling I thought I would just try the switch again, you never know. Happy Days!!! All working perfectly. Now can't get it not to work so don't know what is, or what was at fault. It even works with the old switch so it wasn't that either.
Thanks for your input and diagrams which were all very helpful. I may not have found what was wrong but I do have working Fogs now, and hopefully I do tomorrow at the MOT