Thanks Subbie, but it seems to be more complicated than that! This is an old house and in the last 60 years several changes must have been made to the wiring. There are two extensions, one in the kitchen and one in the bedroom but the colours are not the same as the cables that leave the master socket, so there must be a join somewhere on route....
What I still don't understand is why they all worked for a few days when I put in the new master socket and when I copied the way the old wiring had been done. I could be here for some time.