Please don't mention downloading of copyrighted material, it's against the forum rules. Could you edit your post please?

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

It does sound like traffic shaping but I can't find any info to say that BT are definitely doing this. Have you called them & asked (they might not tell you but then again...)? Some UK providers are only doing this during certain hours.
I'd say you need to call BT.