Looking at your exchange status, it would appear that your exchange is currently being reported as Congested with a provisional upgrade date of October 12th. This means that BT do not currently have their usual amount of backhaul capacity per user at your exchange. There is, unfortunately, nothing we can do about this.
Congestion status on this exchange is RED.
Your telephone line has been identified as being on a congested exchange. If you are receiving varying speeds between 400kbs - 2000kbs at different times of the day this is likely to be a result of the congestion issue.
A provisional date of Oct 12, 2006 has been set for upgrading this exchange.
Hopefully, if BT do upgrade the capcity at the exchange on 12th October, then you'll see improvements following that.