I think they use the Cisco network if that helps.
Contacted ISP both times and was informed BT were looking in to it.
First time it took 2 days second time a week to cure. Speeds increased rarely dropping below 30meg any time of the day, when it did only to about 27 ish meg.
Most of the speed tests in the 20mb region have a massive delay before anything happens then start off slow 1 to 3mb ish, fluctuating 2/3 way through tests then wham and registers that peak performance bearing no resemblance to the connection. Used to have this on ADSL and ADSL2+ with other ISP's.
Actually theres a two lower speeds 20 and 21 May 0.48 and 0.36meg.