antgel wrote:

I want to add a couple of mains sockets to my ring, both next to an
existing one, so that I have three double sockets in total. The mains
cable currently comes from the ceiling and down the wall between the
plasterboard and brick. It is covered in a metal cover, obviously to
avoid anyone drilling into it etc.

My question is - from a regs perspective - as I have to extend the ring
to add these sockets, do I have to cover the cables in a similar way or
can I just run them between the brick and plasterboard with no metal
cover? (I know not to run them diagonally.)

No need to cover (there wasn't even a need to cover the original run,
but it does offer useful protection while the place is being built).
Your new cable runs will be horizontal between visible accessories (the
sockets), which is where wall-drillers should Officially Allow For Them
To Be.

Do try to keep all your new sockets as a ring - extending two doubles
from one existing socket by daisy-chaining is a no-no, and taking two
spurs (to left and right) off one socket is permissible but hard in
practive to get all 4 conductors into the socket tunnels and into the
backbox (therefore hard to meet the 'good workmanship' requirement of
t'Regs). If you've only enough slack to reach a little further, take one
cable to the middle, rather than the end, position, leaving the shorter
one at the current edge - then run new lengths existing-edge to new-edge
and new-edge to middle, if you see what I mean.

HTH - Stefek