does your computer seem to be running OK with other things not online?
If it is then it's a good chance that it is your connection thats slow. go here http://www.speedtest.net and check your connection speed.
I would also as a precaution run a full scan with your antivirus software and if you don't have decent anto spyware software installed download Adaware and also run a full scan with that.
1 other question - have your downloads increased lately ?
it's the "fair use" policy - BT's states that (assuming option 3) you have unlimited download - BUT - if you exceede a (undisclosed) limit .... your connection's speed will be reduced
(this appears to last for a month before being reset)
also - what does your phone sound like - we are in the linefault zone - lots of rain .... cold mornings .... and round us the roadworks bunny is digging up every yard of road.