There is a chance, though I'm told they don't, that Telewest are using their own caching system of pages. Or it could be that they have their own DNS which is out of sync or causing problems.
Do you know the IP address that your domain name resolves to? If so put it into your hosts file and see if that solves the problem for you.
Apparently a DNS record has a TTL value (Time to Live) which can be set to something short or something long (funny that!) If it is set to 1 week (or greater) than it may take a while for that change to be fully reflected. Ideally if you are going to make frequent changes to DNS records you want a low TTL value.
A good old Ctrl+F5 can work wonders even when you have deleted temp files and have set your browser up to check for a newer version of a page every time you visit a site.