Well, im a tad frustrated.
I put the grinder to the pin on the door pillar so i could get the door open. It was then really easy to free up the lock.
Applied loads of wd40, exercised the door lock a lot, replaced pin, shut the door and fine.
Popped out, slammed the door shut and now it wont open again.
[Edited].
Looks like im going to have to change the door lock - not the barrel, just the mechanism. And get the grinder out again.......
Hopefully find one scrap...
Thanks for your advice
Ringo