Sometimes ie on some cars you can use a strong screwdriver inserted at an angle into the catch itself, on the claw side of the lock that moves over and give a hard knock to release it.
I make a point of using my locks every so often manually, but my boot lock comes apart at least twice a year to clean it all out of the debris that gets in there, as it's parked next to my garage roof so all the tile bits/other crap fall on boot and lock.
tabetha