Be careful with F2S. They were an excellent ISP. However they have been taken over by Pipex and performance and customer support has dipped dramatically. BT are interested in buying out Pipex.
It is quite common to wait 1 hour on the support line to speak to somebody. Support is not available through the weekend.
Since Pipex took over, they have introduced Traffic Shaping and on unlimited ADSL, have in actual fact brought a 100gb barrier in without informing customers.
I am also an F2S user, but will wait andf see what happens over the next 3 months, to see if things settle down a bit.

Best thing to do is go to ADSLGuide http://www.adslguide.org.uk/isps/compare.asp

You can compare 6 companies at a time to see how they have been performing. F2S used to be tops, but it has declined dramatically.
The compare button is at ther bottom of the page.
You will get a graphical representation of various performance from these companies.

When you have done that and think you have a couple of ISP's that might be interesting, come back here and see if any mudcatters can advise you on those.