1) Depending on current legislation on new-build private housing mandating a percentage of "affordable" dwellings is pie-in-the-sky. "Affordable" ISN'T, if the price is still 5+ x the average annual wage, or the rent is approx 60% of the average monthly salary.
2) Housing associations have been a busted flush in terms of social housing provision ever since they were tasked with all social housing development in 1983-84. They haven't managed to meet demand (or even half of the demand) in any year since then. They most they've done is nibble at the edges of the problem, and take just enough stress out of the system to stop it collapsing.
3) We've had a fair bit of talk about "council housing" from the pols in the last month or so, but talk, or even action on a grand scale, will still mean a stressed housing system for the next 7-10 years minimum, and I don't see Brown having the stones to delegate enough powers to local authorities to develop and build anything like the necessary amount of social housing, not least because all those "buy to let" landlords, would take a hit, and if there's anything the centrist tossers who call themselves "Labour", "Tory" or "Lib-Dem" won't do, it's aggravate their own.
Shitting on the so-called underclass though, nothing new with that, so it'll continue to be those who aren't "politically useful" who suffer, IMHO.