I have now followed recommendations here and avast is thus providing my virus protection. I shall miss AVG though - it was an old friend - always clear what it was doing with its updating routine and so on. As us free users are not entitled to their technical support, I e-mailed a copy of my first post here to their U.K. sales office in Ireland. I got a prompt reply suggesting that I should purchase a copy when I would then get full technical support. My intention was that they may like to notify their technical department as my problem may well affect a number of other machines - but they didn't tell me that they had. Anyway, if I get any more meaningful feedback from them I will post again.
P.P.