Thanks Dave. Generally (!) the rest of the internet access seems OK. Not only that but using a netbook/tablet (Win10) seems fine.

Definitely my router being connected. I will try replacing cables where practical and generally poking it about!

I do have another router which I guess I may have to resort to, it's just that everything else seems to be fine and I am loathe to go through re-setting-up.

Oh, and a reboot will usually sort the problem out but only for a short time. Strange.

Nick