I use 'The Free Internet' TFI.
Paid £56 for a years unlimitted 0800, I think they now ask around £80/year.
The connection is good when 'on', takes a few tries to get a connection around 6pm or peak W'end times.
The dialer they supply will auto redial up to 15 times if it can't connect - pretty neat.
NOTE : I went through a spell of having extreem difficulty connecting after having moved area. They blamed the local BT exchange limiting 0800 acces through their exchange to TFI's telecom company.
The problem lasted for a frustrating few months then overnight went, and has been fine ever since.
Also the 0800 only works from ONE nominated landline.