Personally, I'd recommend Be (
www.bethere.co.uk). In my experience they deliver on your first 2 points.
Your third point is a little more difficult as it is largely dependent on the distance from the telephone exchange to your house, but with Be you would have 2 choices -
Value package is up-to-8mbps at £14, or if you want a bit more speed their
Unlimited package is up-to-24mbps at £18/month - even if you only get, say 8mb in actual speed, you aren't paying significantly more than for an up-to-8mb connection (and if you're only getting 10mb it means you are a long way from the exchange and an 8mbps connection wouldn't deliver anythingm like 8mbps).
I am on the unlimited package, and I get a pretty much constant 14mb download speed - whether I test at peak time or in the middle of the night. I know others get faster speeds, but they are probably loser to the exchange. I don't know exactly how much I download, but it varies wildly, and some months I will confortably exceed 30GB, other I will get nowhere near it.
I have not been hammered/threatened/throttled/etc by Be in any way - I've been with them since June.
If you can get Be, I would recommend them (depending on how far from the exchange you are).
Another to try would be an Entanet reseller (there are several about, and you should be able to find one easily with Google).
UKFSN (its the only one I can think of off the top of my head) offer an 8mbps 330Gb download (30Gb at peak times, 300 off-peak) for £20 (
http://www.ukfsn.org/home/internet/adsl/maxallowance.html), and pretty much all Entanet resellers will offer something similar.
I know Enta have a good reputation, but have heard complaints about slow speeds at peak times, but then I've also heard they have more bandwidth coming soon to solve this.
Personally, I wouldn't touch some ISps, such as Fast4, Tiscali (particularly Tiscali), BT, Virgin ADSL or Pipex as I've seen too many complaints about them.
Andy