Not sure how common knowledge it is but I only discovered today that Orange UK has an unlimited data plan (with a 250mb fair usage policy) for pretty much the same price as the 6mb plan.

The plans are as follows...

12mths - £12.51
18mths - £10.38
24mths - £9.11

Even better, I called them today to set this up for myself and I got a special offer of £2.50 a month on a 12mth contract. This offer is available until 31st of August I believe.

You can find the plan on the Business Services area of the Orange UK site.

Hope this is helpful