Frostie,
I forgot the smiley!
I had similar problems to you a few years ago - it was always worse in wet weather. After many months I eventually got BT to accept the fact that the line was crap, so they came and replaced the cable from the pole to our house. End of problem.
Also I swore I would not have BT involved when I chose my broadband provider - just as well we have Telewest / NTL / Virgin cable in the area!
SD