The DCLG is expecting huge interest in this. I'm not so sure. Usually 'affordable' means unaffordable, just slightly more affordable, than 'unaffordable.'
http://www.24dash.com/news/housing/2014-05-27-DCLG-expects-huge-interest-in-new-affordable-housing-product#.U4S31PldV8E
Backed with £400M of public money, one suspects a lot of this social housing stock will eventually end up in the hands of BTL.