On Wednesday, November 4, 2020 at 7:49:43 PM UTC, wrote:
A multi-occupier building has, in a communal service cupboard, a
single standard 13A surface-mounted switched socket into which is
plugged a normal-looking plug.

Entering that plug are two different leads connected to two
different items of low-power fixed communal equipment (it is
not easy to see what each of those actually does - or did.

How should that setup be described, on a scale running from
entirely satisfactory to absolutely illegal?

Not quite what you are asking, but you can get (or used to be able to get)
a 'multiplug' - the normal three brass pins but with a larger plastic housing.
Inside the housing the pins came out to brass 'bus bars'. You could fit up
to four cables in one of these, each individually screwed down and with
individual cord grips.

I have a feeling these are no longer on sale, but they were useful items.