I want to fit an MK Masterseal weatherproof socket for powering garden
tools, and will be ordering it from TLC:
http://www.tlc-direct.co.uk/Products/MK56480.html

This will be conveniently attached to the wall immediately "behind" my
CU, so I can take a spur straight through the wall from the
(RCD-protected) downstairs ring. The cable will enter the socket box
from behind.

I take it this can be done using standard 2.5mm^2 T&E?

Also, without having the socket in my hands it's hard to tell: what
'extras' do I need to buy in terms of grommets/glands etc? I can see
several bits on the TLC site! Or is everything I need provided?

Thanks
David