3 also seem to offer an add-on to their pay as you go service where you pay £5 for a month of internet access.

http://www.three.co.uk/Pay_As_You_Go...e_with_Add_ons

In their price guide they define that as 30 days with up to 2GB.

Since I rarely make phone calls on my mobile that sounds extremely good to me. In fact it's better than the equivalent contract which seems to give you 1GB / month.

It doesn't seem to say anywhere if / what restrictions apply (e.g. tethering), but I don't really need it for anything other than web browsing, mail, IM and, err, SSH to my home PC!