Ok, being as there so many replies to my problem and could not respond to all due to time and the news server being down for 3 days, so thanks to all who replied. I decided to follow on my original subject by a new thread, which I don't normally do.
The problem is the actual lock not moving when the key is inserted into it to turn/open the lock. It will move so far, ie key turns about 75/85% and the actual lock does move back slightly, but then key stops dead and is not possible to move mthe lock back any more.
I have tried Ambersil (which is a very thin lubricating oil) by spraying it into the keyhole and inbetween the door and frame onto the lock, but it makes no difference. The lock is solid. Any further ideas? Thanks