I have encountered the same problem today too. Internet working fine last night, but today I can only view proone and google. Other websites will not work and I can't send or receive email. 3 computers in the home all have the same fault, and I've checked the router settings.
3 calls to Talktalk in Bangalore with 3 different reasons. 1. a firewall problem. 2. a local internet fault at my exchange and 3.they are uprating my internet speed and this has caused the trouble.
Gonna sleep on it and see what happens tomorrow, but you are not alone renfrew.
P.s I see you too are in Glasgow, so it may be a local fault. I'm in G41