The boot lock has a failsafe designed into it,the key is supposed to turn in the lock and it depends on how you want it to open. When the slot in the lock is horizontal the lock is opened and closed by the central locking, When the slot is vertical the tailgate is locked all the time, and can only be opened by using the key in the lock. To unlock the tailgate put the key in the lock and turn it fully to the right, hold it in this position and press the lock button in, the tailgate will now open.
The central locking system uses air and when you get the boot open using the above procedure you remove the panel on the boot and you'll see on the right a blue actuator, this is a vaccum solenoid and is what locks and unlocks the boot, On my car the boot lock didnt work and I found it was the little clip that holds the rod from lock to solenoid had come unclipped so when operated the arm was bending up not pushing. when clipped back on it worked fine, have a look and see what happpens when you look the car with the panel off and boot open.
