pm Mk1RS2000. He was having a similar problem, but I can't remember the exact details. But he found a chafed wire to the central locking was shorting out. Might or might not be the same, but he'll be able to give you more info.
I have also STILL got this problem, have had it for two weeks now, Ive also put a new fuel pump relay on. i think it is definitely something to do with the central locking cos i fiddled with it again and it came right and the car started (wahay)
I came to it the next morning and same thing, passenger door wouldnt open and car wouldnt start!
so could you please tell me if you have any success