Have you checked your IP Profile by running the BT speedtest?
http://speedtester.bt.com/
Wind/rain can affect the speed you sync at. BT will then lower your IP Profile. Even if you shortly after sync back at your normal speeds it can take BT 2 or 3 days to raise your IP Profile again.
jelv
Plusnet ADSL PAYG Jan 2004 - (current)
Plusnet Dialup Nov 2001 to Jan 2004
Previously Compuserve, BT & LineOne Dialup