I'm not running a separate firewall program, just the XP one, so it is unlikely to be that.
I have also rebooted a number of times with no change in the situation.
Looking back on the previous 24 hours to the time when everything worked ok I can think of nothing that would have caused the change. I visited Pprune a couple of times, read a couple of online newspapers, and read the BB online news.
It baffles me as to why changes like this suddenly take place without any imput from the operator.