May not help but here is what happened to me.....been with Pipex for a number of years and had a 1 meg connection for the last yr. All was fine until about 6 weeks ago when the speed went slower than a 512mb connection....went round and round the calling/holding at pipex....have you done this/that etc....did the bt speedtester and proved that the problem was not the line and pipex insisted connection to bt speedtester left on so bt could diagnose....5 days passed and I was called by bt engineer who said he had just done a remote test to the PC and could I check if any change....no I could not as the PC had just crashed (win xp sp2 and never given a problem before...coincidence?!!)
After much work from my end PC up and running and speed stable at 1mb.
Called pipex again to say not best pleased and tongue in cheek talked about migrating....."if we reduce your bill by £5 per month and double speed to 2mb will you stay for another yr?" I was asked.
So still with pipex and speed consistantly high at 2mb.
Good luck!