Many thanks for all your responses!
I really only surf off-peak so the clara.net option looks to be the best.
Thanks for your suggestion AquaPlane, but I don’t think my IT skills are up to fiddling with my Dial-Up software!
BT continues to be hopeless – last night was an absolute nightmare (about 20 mins actual surfing in a 2 hour period) – so I’m off for a word with clara!