I'm about to re-wire the study which has a number of PCs and other kit
with "leaky" PSUs so I've been reading up on the "Regs".
Whilst I *do*
understand the rationale behind the requirement for the
double earth terminal in double sockets shouldn't there be a similar
requirement for all terminals in all sockets in all applications?
If there is a danger of two cables into one screw connector coming
loose then surely this applies to all circuits; phase and neutral as
well as earth? Whilst the loss of the CPC (earth) could be
immediately dangerous surely the splitting of a ring circuit with
consequent overloading and localised overheating at the point of the
bad connection is also of concern?
If the earth problem is mainly caused by two cables into one screw
connector then why does 607 allow single socket outlets at all? 
I've had a look at couple of catalogues and dual-earth fittings are
only available in double sockets.
 and seems to imply that they are preferred as the use of doubles
with dual earth has to be an "exception"
(Please put out the cats to reply direct)