Fast internet connection for 24 hours only in London?

Does anybody know of a place where I can get/use/rent a FAST internet connection for about a day in/near London? I have a big backup that I want to seed to my backup provider, and so having a 20+mbit connection that I could use just for a a short period would be fantastic. My home dsl line is only 256kbit and I don’t want to buy a whole new line just for this one upload. I could pay by the hour or day or something. Do any shops/people do this?