Alan, really weird, but having read your post and despite having checked fuse, for some reason I was drawn to taking another look at it. (Had already tested fuse with test lamp power supply in and then power supply across fuse which indicated fuse not blown).
Removed fuse and tested across battery with test lamp and to my horror not working! There was a crack in the fuse leg.
Feel very embarrassed. From now on will remove every fuse before passing it as working. Could have lied but decided to come clean!!!
Lesson learnt, problem solved.
Without your help lads, I would still be tearing my hair out on this one (whats left of it).