FYI All O2 have some new packages. They are a bit of a comedown from the old ones.
http://www.o2.co.uk/broadband/
The Basics - 8Mbps Down, 1.3Mbps Up - 13GBP/Month (8GBP with O2 mobile phone) - 20GB/month cap.
The All Rounder - 20Mbps Down, 1.3Mbps Up - 17GBP/Month (12GBP with O2 mobile phone) - AUP kicks in at 100GB/month
The Works - 20Mbps Down, 2.5Mbps Up - 25GBP/month (20GBP with O2 mobile phone) - AUP kicks in at 250GB/month
The last 2 are being sold as unlimited subject to AUP, basically it's a soft cap - they can choose to harass you at 100GB and 250GB/month respectively or not at their discretion.
There is also protocol based shaping (Yes Sirius, using DPI!!!!

) on these packages for the first time.
Details
here.
The shaping is applied to streaming and P2P downloads, I think it's also being applied to Usenet and Rapidshare-type download sites - will confirm.
Those of us that are already customers remain on our current uncapped, unshaped packages and are grandfathered.