You should be able to fool the door to thinking its locked. Just click the door catch with a screwdriver until it clicks twice (with door open) then try the central locking. Just remember to unlock again with inside door handle before you shut the door properly or you will break it. If its not lining up this may have already happened.
I think the door catch is already knackered, it's hard to explain how it behaves but basically it doesn't move to allow the door to catch on, it just sticks and the door then smacks against the metal catch, I have to manually move the catch out of the way in order for the door to actually close