ive been with BT for years now & ive got the 8mb service (£25 pm + vat !!!!! ), the fastest its ever ran at was 4.5mb but for the last year its been really slow, sometimes its even dropped as low as 0.3mb

but i think this is because i do a lot of downloading & they capped me, even tho they advertise an unlimited service, they brought in the fair use policy, basically if you download between 5pm & 10pm, they slow you down to a snails pace, the tech phone numbers also a joke, your put through to india & its a bitch trying to understand them !
overall, the service is reliable if you dont download much but theres better providers out there.
my gfs with virgin media & has the 20mb service for £20pm & runs at about 14mb, still super fast