Hi,
First of all, thanks for the replies.
No worries on the rear brake. It gets turned around when I build up the bike.
The number stamped on the rear drop out seems most likely to be the serial number going by other Raleighs of similar vintage.
It's a Worksop made frame if you believe the decals. So a subcontractor seems unlikely.

I had not thought of a number stamped after the fact, such as a licensing or registration number. I suppose that could be.
Just one of those things that makes you wonder why, especially when no quick answer is found on the various bike forums.

Pete