It's the greed of the girls who set the price. Diva have a baseline price and also a target for how much of a cut they take (as do all agencies like Diva), but it's the individual girl who sets her price.
From what I've gathered, most of the girls have managers who recruit them, bring them over and hook them up with the agencies who act as advertising and switchboard, the managers set the prices, they are the biggest mouth to feed, the agency percentage is an additional cost. There are a few independent girls who just work with the agencies direct and price themselves according to where they feel they fit in the market at the time.
I see a few of the top end girls direct and pay accordingly, they tell me that even the £1,000 an hour price point is popular enough with punters willing to pay and the girls themselves feel generally entitled to charge these fees now, even though pricing has doubled over the last few years, it's remarkable and painful for punters. Personally, I won't go above £400 which is £150 more than my limit two years ago.
