Apologies for using Google's broken implementation of newsgroups...
Anyway, from looking at
http://web.ukonline.co.uk/freshwater/bterm.htm,
the 15cm diameter round box I was referring to looks like Block
Terminal No.17 (very ancient looking). The "tired looking adapter" (see
above) could be any of Block Terminals 77A to 89A, which are said on
that web page to be suitable for use inside only, whereas mine is
outside.
Also, I have been reading more about the fact that sometimes multiple
master sockets are installed but that this shouldn't be done, except
maybe you can do it if you really know what you're doing. I do appear
to have at least two masters.
I wish I hadn't looked at all this now. What a horrible set-up! Now to
look on the Price List for:
1.Replacing Stone Age external Block Terminal.
2.Running new wire up house and in through a hole in the
newly-decorated study wall, and there fitting a new Block Terminal
inside the flat, where it should have been in the first place.
3. Fitting new Linebox
4. Fitting customer-supplied Clarity faceplate (less allowance for tea,
biscuits etc.)
5. Replacing three extension sockets, wrongly fitted as Master Sockets.
6. AOB?
Have I left anything out?