Thanks for all your comments.
More puzzling still - after reading the posts above, I tried starting Opera 12 again, did not re-install, just used the installation 30 had (fortunately) left behind. Amazingly it all works just like it used to. AFTER it was working properly I ran Spybot and found 4 instances of Ilivid, which Avast had failed to get...
What was all that about!