The apple online store itself says it's available from O2 and CPW - conspicuous by its absence is any mention of it being sold by apple stores.
The PayG is not coming out on the 11th.. that much is known - walk into *any* O2 store and it clearly says PayG later in the year, and CPW have emailed everyone to tell them it won't be available.
That means unless the apple stores get the ability to sign people up to contracts (which is possible but I've not seen any evidence of it so far.. no real advertising in the apple stores for example) they will not be selling it on the 11th. They'll wait until PayG release.
80% chance that it wont be on PAYG but you dont know that for a fact.
The leak of prices, the lack of info suggests the stategy has not yet been decided!