I care, Clive Sparks! I have learnt how to partially use a multimeter, and established that my assumptions were correct in terms of which wires were which, but perhaps not their true function as it stands. I will switch the switch-line and the switch-feed and let you know. As you say, it can't do any harm. Despite what some people maintain. I'm not fiddling around by guesswork, as some would suggest. I'm trying options suggested by other people on this forum, whose pro-active responses are much appreciated.
Sorry for not also thanking you before, bernard, for your earlier post.
If this option turns out to be correct, then am I right in thinking that a better long-term solution would be to then reverse the two wires in question at the ceiling point, so that wires in the switch are doing their "proper" job in terms of their colour coding?
P.S. My interpretation of Plan B appears to work, even when I try to stop it. Many Thanks, gents.