Hrm, diagnosis could be a bit trickey here, you need to be able to unplug the wiring harness from your door locks, but at the same time be able to lock up the car via the central locking.

I cant remember if the boot lock allows you to do this... if it does, pull the wiring from both your front door locks and then lock the central locking via your key in the boot...

Can anyone comment as to whether the door locks and the central locking motors are electrically separate?

As a side thought, you could have water in there causing a short...