The consortium has refused, saying it has already offered to provide £120m worth of infrastructure to the council, in the form of roads and street lights.
Roger Madelin, chief executive of Argent Group, said: "[Paying for the affordable housing] is not an option for us. The local authority has got to work out what its priorities are. It will have to arrange the housing subsidy from another source."
Camden intends to hold firm on its decision. A spokesperson for the council confirmed that supplementary planning guidance, due to be completed in the next few weeks, will still prescribe 50% affordable housing.
Camden's cabinet is due to vote on the guidance on 17 December. This follows a consultation on a draft brief that closed on 10 November.
The 1800-home development will include offices, retail and commercial space, and incorporate listed ex-railway buildings.
The 53-acre scheme is likely to be an important test case of whether London councils can enforce the 50% affordable housing target set out in Ken Livingstone's London Plan.
Work is not scheduled to start until January 2007.