There is certainly a demand for Agencies in London, some have been around for many years. For me there is no advantage to going through an Agency unless a WG i fancy is only as far as i know available through them. This scenario occured last in 2009 and the Agency were a bunch of lying cunts. I count them out of my punting nowadays.
An Agency might be open 24/7 or very long hours so that is an advantage to some punters, i can wait till Indies are available myself. Agencies or some at least can offer a choice of WGs immediately in theory, again i can wait till an Indie is about.
Thats about it, so in exchange for these advantages i would have to pay a minimum of £150 an hour to go through a reputable and well reviewed Agency with feedback. Its not VFM to me when i know i can punt with good Indies from £70-130 an hour and slap bang in Central London is HOD South Kensinston who presumably make a profit yet charge £120 an hour and have WGs i have punted with at Parties and that are highly rated by FRs and by feedback. So they have 2 WGs on per day in their Parlour but dont open weekends. They just prove to me the utter greed of Agencies in London, many of whom charge over £200 an hour. A Parlour also offers a WG the premises and in theory due to numbers a safer environment so in theory they should charge more than an Agency to the WG who rarely offer the premises, the WGs uses her own or a hotel and like an Indie works alone. Yet the cut is often the same with both, a third of the WGs fee to the Establishment, sometimes with Agencies a half. They will always get punters, be it the mug punter, the tourist punter or the rich who doesnt care what he pays punter, or punters like NIK who has found a gem in Nicoletti (may be wrong spelling) and sticks with her as he knows she delivers every time.