In their report on the coalition battle over Regional Development Agencies (Eric Pickles wants to scrap them, Vince Cable wants to keep them) The Economist says:
Cuts to London Development Agency’s £320m budget are being negotiated separately.
The LDA's money includes £53.5 million on admin, £29.3 million "marketing and promoting London", £37.5 million on a programme to "address barriers to enterprise", etc. Of course the real barriers to enterprise are heavy taxes and heavy regulation.
I don't know who is involved in the negotiations. Perhaps Boris Johnson sees defending the LDA being funded by Whitehall as part of his job to "bat for London." He would do better to suggest a nil budget for the LDA – in return for money continuing for things that matter, like Crossrail.