Many thanks Pentoman, that's answered a couple of questions.

Given that the 2nd door plunger switches are to enable the windows to be operated with the ignition off, it is a puzzle why it is affecting the operation of the central locking also. However, they are both fed from Fuse 12 (which is always live). which may be a clue.

The answer to the puzzle lies in my first question I think and I'd be grateful for any ideas that anyone may have...

Q1. What is in the circuit between Fuse 12 (in engine bay fuse box) and the central locking pump 12V feed (under the back seat). I now suspect that there may be a relay somewhere but I'm just guessing.

Thanks, Pete