I've not done a wide survey, but I'm very pleased with Flyer Internet. 0845 number to access, and everything free thereafter. I've been using them for my "mobile Internet" for several years, and been much happier with Flyer than with my previous pay-monthly ISP (now cancelled).
The only slight drawback (and all the free ones are the same, as far as I know) is that you can't update your website while using a different ISP connection to the Internet (eg ADSL if you have it).
I've set up most of the local clergy round here with Flyer Internet accounts, and all are blissfully happy with them.
For more information,
http://www.flyer.co.uk/ and click on the "FLYER ISP" tag on the left.