John,

but I doubt they _can_ be miswired [and still actually appear to work]

As english sockets are constructed in such a way that the plug can only be
inserted in a single orientation and therefore most likely only switches the
(supposidly) "hot" wire, it would be easy: Just swap, when wiring the
socket, the neutral with the phase wire. And as (re-)connecting such
sockets can be done by the man of the house himself (or a bungling
electrician) ....

The circuit will still be open when "switched off" (no current can flow,
causing the attached device(s) to stop working), but the "hot" wire will
still enter the attached device. Worse, over what is assumed the neutral
wire ...

An extension _lead_, of course, which may be _feeding_ some switched
sockets, certainly _can_ be, of course.

Nope. Not when the single-orientation wiring is followed (which is
ofcourse subject to the same mistake as above).

Regards,
Rudy Wieser