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Cheers all for answers - very informative. Guess what, we live in a very rural area, only about 10 houses and our leccy definitely comes in via overhead cables (we have one of the poles in our front garden) but don't worry, would get a prof. to do any work, would not mess with electricity myself (although will attempt most other things).
Interestingly, yesterday the RCD switch tripped and there wasn't a storm... again it was the ring main, and again, more precisely the tv socket causing the problem. This plug had four things plugged in via a 4 socket extension lead. Got me thinking as to whether the lead is faulty? Or all this stuff is overheating in the heat? So I've plugged the video (not used much) into a separate socket which will be kept off unless we need it, and plugged the remaining three things into a different extension lead. Will see if that helps.