Andrew,

Thanks for the reply.

MK part is 735WHI.
The plugs themselves overhang the sides so they won't be
a lot of use if the plug has to go in an equally narrow
space as you won't be able to get you fingers on it to
pull it out.

The plug will need to come out only very infrequently, so as long as it is
actually possible to remove it, a bit of awkwardness won't matter over
much.

MK also do a smaller surface mounting socket, 74x64mm.
I suppose you could sink the surface mounting box into
the wall, or make up a appropriate one some other way.

Yes, that's obviously worth investigating too. Thanks.

Bert
http://www.bertcoules.co.uk