Adam wrote:

http://www.gtectraining.co.uk/images/back%20boxes.pdf

is the best link I can find.

Interesting document, thanks Adam - but all this convolution as to whether
the back-box has no fixed lugs, or one fixed lug, or two fixed lugs; and
whether the socket outlet has no earthing strap, or an earthing strap and
one eyelet, or an earthing strap and two eyelets; and whether the back-box
has been mounted the right way up, so that the fixed lug corresponds to the
eyelet on a single-eyelet socket outlet, or whether the customer will accept
their 13A socket mounted upside-down so that it does. Good grief, what sort
of committee wrote this ridiculous, labyrinthine precept?

What if someone (e.g. the householder) replaces a double-eyelet socket
outlet at some future time with a single eyelet socket outlet and ends up
with the eyelet screwed to the adjustable lug? What if the socket outlet
mounting screw(s) become loose?

As back-boxes (flush or surface) are classified as 'exposed conductive
parts' and are therefore required to be earthed, surely the short answer is
to ALWAYS install an earthing tail between the socket earth terminal and the
back-box?

I think I shall continue to pick-up the back-box earth terminal with the
(uncut) earth core in the T&E ring main cable, as I described in my op.

--
Spike