Apart from the specified clamping force, these just look like the
standard crimps that I have been using for years for bodges on old cars.

They are the same. The differance is that with mains you don't bodge
it. You use the proper tool

Once the connection is crimped, and presumably, insulated with heat
shrink tubing, is there anything to do other than plaster over?

No

Does the joint need mechanical protection i.e. a metal box with a cover
before plastering? Or is the plastering deemed to be enough?

Provided it is the correct zone it doesn't need additional protection

How about the soldering option. Is a suitably twisted pair of wires, to
ensure mechanical strength, then soldered and insulated as above OK?

In principle yes. But it is not easy to use heat-shrink sleeving in
this circumstance. You need to take the outer sheath back a fair way
to get the sleeving onto the inner core. And there is a danger that
the heat of soldering will shrink the sleeving prematurely


Sorry, too many questions!

Steve