Both the developer and HBG are remaining secretive about the scheme but project sources said the contractor was preparing to seal the deal.
The eight-storey building will be used mainly for offices and retail.
In the basement there will be parking and a health club with a swimming pool.
The planning application also includes 22 town houses at the back of the development, some of which have been set aside for affordable housing.
Marks & Spencer, which last week announced a 20 per cent rise in interim pre-tax profits, has been at the site since it was built in the 1957.
Last year the firm moved to a smaller base in Paddington, west London, after auctioning off its remaining desks, chairs and 60 mannequins.