Thanks for reply, CH. Yes, if you turn off it's usually OK again for a few minutes when you switch back on, I think. Actually, it slows down in work too, but not as much (if I remember correctly). I'll have to investigate further and get more details. I just wondered if it was a Yahoo thing other people had found.
Just an update. Yahoo mail is sometimes very slow in work too (which is normally a quite fast connection) so I suspect it's a Yahoo thing. It seems to be linked to their animated adverts - I'll have to see if I can turn 'em off. But nobody else has reported any problems???