In message , jerrybuilt
] writes
There will probably be an earth wire to run to the metal box,
too.

The probably isn't one there if these sockets have been mounted on
plastic surface mount boxes, but one should be installed.

Get some earth sleeving (yellow/green plastic sleeving) and use a scrap
piece of earth cable from a length of the same sized cable.

[1] Someone will soon tell you all about a thing called an SDS
drill, I'm sure. If you can't get one, they are not vital!

Once you've used one once you soon realise that they are almost :-)

--
Chris French, Leeds