Do you only have one ring?, handy to have 2 for just such an occasion as
this, also this would be on of the few acceptable situations to use an
electric iron wired up to a lighting circuit adaptor.

No, just one ring. I don't have friendly neighbours. A 50W iron would
(according to my calcs) require an extension cable of handling around 5
amps. I don't have one of these.

Ok, 30s is way too long, if you haven't made the joint in 5s then your
iron
isn't powerful enough and you risk overcooking the joint/insulation. The

Well, it's done and, if what you say is true, I'm well and truly f***ed. The
joints have been made and if the insulation has been damaged then it's
damaged forever. It's hard to describe the situation but the solder joints
were made just after the T&E comes out of a concrete-cladded wall. In other
words, I can't cut back and start further up.

The problem with overcooking the work is less likely to be in the current
carrying capacity of the joint but in the integrity of the insulation
which may
break down after a few years of ageing, not something you would want to
have buried in the wall.

Tell me truthfully - is this something that *really* happens in real life?
I'm not being trite - I really want to know. Does anybody have any actual
experience of it happening?

As other have said, no-one can say authoritatively that your joint is good
so it may be worthwhile remaking it after a bit of soldering practice and
using the right sort of insulation.

I've got some small experience of soldering and consulted a pal, and I'm
sure that the joints are good enough, both mechanically and in terms of
soldering. The ring main is almost certainly functioning correctly.

However, the problem is whether I've left a serious problem for future
owners of this house by

a) using electrical tape to cover the joints (answer: yes)
b) degrading the insulation to the extent where it will catastrophically
fail in a few years' time.

I think my only real solution is to put these joints into blank socket boxes
accessible to anybody, so at least a future electrician can open them up and
discover what's been done. This will look ugly (the joints are at head
height), but I guess I can strategically hang some pictures over the boxes
when it comes to sell the house.

I'm sure this sounds like a lecture, its not meant to, good luck :-)

Lectures are sometimes needed for those of us with more enthusiasm than
experience, and your help is received with thanks.