David Hearn wrote:
Can anyone advise what depth backbox I should use? I'm adding a 2G MK
socket, and was planning on using 25mm - however after reading the
instructions it said that for = 9mm face plates, use 25mm, and 9mm use
35mm.

I think MK have two specific ranges: sockets which have thicker
faceplates and can be accommodated in shallower boxes, as well as
standard ones with thinner faceplates that need deeper boxes.

The deeper box the better.

The boxes should be sunk so that the edge of the box is flush with the
finished wall surface or near-as-damnit. It's not too critical with
plaster, but if a wall were to be clad with a timber-based panel a gap
between the box edge and the faceplate might mean the terminals failed
to be enclosed in a non-combustible enclosure.

And boxes are usually fixed in with a couple of nails and a prayer, but
two No 6 screws (with the slots lined up :-) makes a diypersonlike job
of it.

Owain