Thank you once more, The Flying Pram. I don't know why but since Sunday my Flash plugin has started working (so far as I can tell, anyway) perfectly once more. I have done precisely nothing apart from observe.
Perhaps all of the experts on here knew that was going to happen..... I can't think of any other reason for the silence of all but TFP because I don't think I've done anything to upset anyone! Perhaps it's because it's holiday time.