High usage broadband account - know of one?

Got a snotty letter off my isp for going over fair usage limit (40gb/month)now i worry about about downloading movies and music etc and where i am in bandwidth. is there an isp that will for example bill me £20 a month and them charge me per gb if i go over a set limit?dont mind paying sort of £30-£40 a month is the package is right. thankyou in advance
Answer
I am with pipex. i pay £30 a month. unlimited broadband, unlimited free phone calls except mobiles.