I'm after what we used to call a "safe block" - although I think that
was a trade name.

It's a quick way of applying power to something that only has bare
wires on a trailing lead.

A safe block is 3 spring loaded clamps in a small box with a hinged
lid, and attached to a trailing mains lead with plug. (but no power is
applied until you close the box lid, so no exposed live terminals).

Anyway, it would be useful to apply power to pumps and valves in my
central heating to make sure they're good, before the fixed wiring is
done.

Anyone name a reasonably priced supplier, or products that fulfill the
same function but go by a different name?