OK, thanks for that, sounds like he "broke the rules", though it was a while ago could they have changed?
I definitely was there and would have preferred a complete rewire, but I wasn't asked.
There is no problem getting the cable to the master socket, it's just inside the front door and the overhead cable terminates almost directly above it.
Would have involved drilling a new hole through the cavity wall to do it tidily as the old cable is somewhat buried under plaster and redecoration from the intervening many decades (about 4 I reckon - 40 years) since it was installed in probably the late sixties when the house was built.
Anyway, beginning to digress somewhat from the OP's topic so I'll not divert further.