Andy,

Thanks for the reply.

Looks to me that the outer rim would "pop" off, leaving the circular
part raised, and the screws to the sides of that?

Yes, I wondered about that. It does seem the likeliest solution.

Brushed chrome finish it says? Crushed coal more like!

For the actual socket bit, you mean? I rather like that - a pleasant change
from the usual white. It's hard to judge the outer housing (which
presumably is the brushed chrome bit - I wonder what they brush it with?)
from the pictures.

I think I'm going to give these a try in my new kitchen. I hate chasing out
for sunken wall-boxes, and especially trying to get two or three to line up
neatly next to each other.

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