The other day I was looking for some 2-gang 13A sockets. I have always
been used to reasonably decent ones and they have always had a metal
eyelet in one of their fixing holes, connected to the earth bar. While I
was looking, I was suprised to find cheap ones that did not have this
feature. I can see people using these as a direct replacement for paint
marked, old sockets without thinking of adding a connection to the back
box's earth terminal and therefore leaving the possibility of a fault
making the back box and hence the contactable screws live.

SteveW