BT are known for traffic shaping & might also be blocking p2p in some areas (?). If you use the forum search to look for BT homehub, BT voyager you should find some older threads.

To start off with, try changing ports. In LW go tools > options > advanced > firewall config. Change LW's listening port to 64049 (you can also try other ports in the range of 49152 - 65535) > apply > ok.

Make sure that your XP firewall's off if you're using the McAfee firewall (2 software firewalls together will conflict). Also make sure that your McAfee firewall's configured to allow LW.
Port Forwarding for the McAfee Security Center

You could also try port forwarding for your router. The instructions are here.
Port Forwarding for the BT Voyager 220V
Don't forget the step of setting up a static IP address. LW's listening port, port in the 'manual port forward' box & port forwarded within a router must all be the same number

See how you go with that. If the problem's with BT, there's probably not a lot you can do. But try those suggestions first