For all his talk of creating a Stratford Guggenheim, flipping the lid on Zaha Hadid's iconic aquatics centre to fit a curly-wurly slide and building an equestrian centre in East London, there is little that Boris Johnson can change in the 2012 blueprint.

The bulldozers are in, the 20m-deep concrete pilings are in under the proposed £525 million stadium, and the opening on July 27, 2012, is in everyone's diaries.

The mayor may give the impression of someone who wants to return to the drawing board but it is political noise. In reality, he can only pull at the edges of a £9.3 billion project that was well under way before he won office.

What Mr Johnson is achieving, through the bluster, is a sharp focus on accountability and, that overused buzzword, legacy.

A shake-up of the old order is welcome if it means that Olympic chiefs cut their cloth to fit the budget, rather than leaving things so late that cost overruns are unavoidable.

The mayor's £300 million contribution, which became the subject of such confused debate on BBC radio yesterday, is a red herring: it is accounted for by the London Development Agency's £1.97 billion funding commitment agreed in March last year.

What is clear is that it cannot come from council tax or fare increases, and the mayor has ruled out further taps on voters' wallets. His argument with the Government is that, should its £2 billion contingency fund not be spent, London taxpayers should get some of the £300 million back.

It is a moot point. Even the most optimistic politician does not expect to find any loose change down the back of the Olympics sofa. Least of all Mr Johnson.