First of all have to agree with Midimoto regarding AO (Hel)L and Syphus regarding 2mg D/L.
Unless you're intending downloading large files eg Music files or films (Tut tut, slapped hands....Piracy) you wont see any improvement over 512k or 1meg speeds.
Also, unless again you're intending on downloading large files, you shouldn't be too fussed about download limits 2meg should be ample for the average user. If you exceed it you can always upgrade it at a later date.
As for which ISP......well thats a matter of personal preference. I know poeple who swear by AOL, personally I dont and have switched from them to BT (complete with home hub, Oooooh how posh. lol) Others to consider are Tiscali and Pipex or if you've got cable Telewest and NTL. Personally I wouldn't got with Wanadoo or whatever its called these days because I've heard some bad things about connection problems etc. If you check out this site:
Compare UK Broadband Providers Online it might help you decide which to go for, but as I've already said its a matter of personal preference.
Smirnoff