Try downloading a file from here & see what speed you get
http://www.magnetmix.com/video.shtml

If those files download very slowly then your ISP might be using traffic shaping measures.
I can't find anything to say that Blueyonder are shaping but...they're part of Telewest, which is part of NTL & this article suggests NTL have begun shaping during peak time (confused yet?)

http://www.dslreports.com/shownews/79795

Try changing ports. Within LW tools > options > advanced > firewall config. Change LW's listening port to 64049 (or another between 49152 - 65535). You'll also need to change the port forwarded thru your router and the number in the box next to 'manual port forward' option on that same LW page. All numbers MUST be the same

Have you tried downloading at different times of day/night?