Thanks, Toto!
That's very interesting. The problem for me only seems to have occurred after an upgrade to the 2Mb service about three months ago. I have tried rebooting the NTL modem several times since to get a newly assigned IP address but it hasn't made any difference.
Well, at least there's a hope of being able to work again! I guess I'll have to investigate my home setup some more....
Thanks for your help,
Paul.