Was the previous locked condition Superlocked??
If not, try very carefully levering the top of the window frame and use a stiff wire hanger or similar and try to lift door lock....else a good locksmith could help.
The AA have been known to get in a non-superlocked P38, but one report on here, said the AA man snapped his key somehow...still not sure how...!!!
If it was superlocked, then that is a whole different ball game which will require a Brixton/Cardiff/Newcastle key (a large brick).....
It may be possible to get in when superlocked, but I have not heard of a non destructive method, although I do stand to be corrected.