Lewisham Council has trumpeted plans to build new homes - but a report shows it wants to flog 20 per cent of them to private buyers.
The new properties - the borough's first social housing since the 1980s - were initially promised in 2012 for delivery over the following five years and were a central plank of Labour's election campaign.
However, a report for next week's housing select committee states for the first time that 20 per cent of the homes will be sold-off, with the surplus "re-invested in the delivery of more social housing."
Lewisham Council now says that proceeds from around 100 homes being sold will help build 500 council homes instead of the original target of 250.
But Daniel Strange from campaign group Lewisham Defend Council Housing said: "We think this is an outrageous decision at this time of dire housing need, and appears quite duplicitous after this development and the council's housing promises were a big part of the local election imagery - lots of shots of the mayor in front of the site hoardings, for example.
"We'd like the council to explain this and reverse its decision to play at being a private developer."
Work has started on the first six new houses, due to be ready next January. There are plans for more to follow with 23 in Forest Hills' Longfield Crescent and another 18 in Woodvale.
The council also wants 32 homes in Blackheath's Dacre Park and Boone Street, 22 in Achilles Street, New Cross and a further 15 at Blackheath's Lawn Terrace.
But Mr Strange said: "The most critical factor in the local housing crisis isn’t a lack of properties to buy, but the lack of properties to rent at truly affordable levels."
A Lewisham Council spokesman said: “The council has now agreed a new target of 500 new council homes in the next five years. And we will pay for these additional council homes by building a small number of homes for private sale.
“It is by ploughing the sales receipts from these private homes back into the homes for social rent that we can be more ambitious with our council house building programme. That’s a win for families on our council waiting list and a win for those wanting to buy their own homes.”