John wrote:

I can just visualise the sudden leap in Dymo tape sales for all the "This
socket is double pole switched" labels that are going to be "required"

Bear in mind though that there's no requirement in BS 7671 for any
'means of isolation' to interrupt the neutral conductor, *except* (a)
for the main switch in a household installation, and (b) for any
isolator in a TT-earthed installation. (If the main switch doesn't
isolate the neutral there should be a removable neutral link, and this
is common practice in industrial 3-ph installations.) [OSG sect. 5.1, p.34]

I doubt that the switch on /any/ 13A socket, whether SP or DP, could be
classed as an isolator, due to its not meeting the requirements for "the
position of the contacts to be externally visible or be clearly,
positively and reliably indicated." [476-02-02]

--
Andy