This sounds like a DNS issue. Some things you can try, try to ping
www.google.co.uk and see if it responds, or you get a time out. If that doesn't work, I suspect it won't, try to ping 72.14.205.104. If that works, that is the IP address I get when I ping google UK, then it is a DNS problem.
I would also guess this BT hub modem is a router as well. You may have to look into the config to see if it will pass DNS addresses back to your system. They get stored in /etc/resolv.conf. You can try storing correct DNS server addresses in there, some distros will overwrite what is there, so it is not permanent. Distros differ where these values get stored so they are not overwritten. I use Mandriva, and on here they go in /etc/sysconfig/network-scripts/ifcfg-eth0 for eth0. You may have to look at some doc to find out where to store the info...