It sounds to me like the barrel of your lock was/is stuck in the locked position and in order to operate the lock the previous owner has glued the bolts on to the cylinder so that when depressed it pushes down on the catch. You might find that your key and lock don't even match and its only the central locking that has been locking your boot.

Mine ceased a few months ago and I got a brand new lock and had it matched to my key from a guy on ebay. He offers a repair service too but mine was totally fooked. It's a bit more expensive than the scrappy route but I didn't want to have two sets of keys.

Search Ford Lock Repaired and you will find him.

Hope that helps.