But we have known this for a long time in East Devon where even enormous schemes are allowed to build without any affordable homes at all:

http://www.bbc.co.uk/news/science-environment-30009901?

though coincidentally it appears to be the case in South Somerset too:

http://www.westernmorningnews.co.uk/opinion-Catch-22-planning-rules-holds-councils/story-24570865-detail/story.html