symptoms;
if door is open and and nib is up, when you shut door it automatically locks and nib goes down.
if door is shut and you are trying to get out, pull nib up, VERY stiff, if you let go, nib shoots straight back down. to get out you have to pull nib up whilst opening the inner door handle.
Door shut, from outside. Put key in lock and turn, VERY stiff almost a worry the key will break. you can see nib rising, if you let go of key nib goes back down. to get in you have to turn key and pull on outer door handle.
what i've done allready
Removed outer door handle cleaned and regreased, This moves fine and free
Disconnected central locking actuator, still same fault
removed catch fitted to door, cleaned and regreased. Still same fault
I think it is this catch

Any other thoughts before i go get one?
Cant imagine a central locking door catch being easy to find, or cheap!
cheers, Lloyd