John Borrman wrote:

Cheers for that, rather fabricate an earth than replace all the boxes....

IF we're talking about flush metal mounting boxes that are sunk into the
wall (i.e. not accessible when the wiring accessory is in place),

AND the wiring system is twin-and earth and, explicitly, is NOT MICC or
metal conduit, where the earthing is provided by the metal sheath of the
cable or the conduit, via the mounting box,

AND the metal face plates each have an earth terminal,

THEN it's OK to connect all the incoming earth wires to the faceplate
terminal and there's no specific requirement for a separate earth wire
to the back box. The box (which is not an exposed-conductive-part in
these circumstances) will be earthed via the accessory mounting screws.

--
Andy