Construction started on the £1.5bn redevelopment scheme last week and L&Q is now on board to provide affordable housing.
L&Q will provide 54 affordable homes at Trafalgar Place on the Heygate Estate from a total of 235 in the first phase.
The first new homes are scheduled for completion in 2015.
Lend Lease project director Pascal Mittermaier said: “The regeneration of Elephant & Castle is now gathering momentum both in terms of the progress on site and the sale of new homes.”