Going to have to be some building programme to cope with the c.700,000 per year birth rate plus net immigration.
That aside, allowing benefit payments to be used against mortgages is partially a good idea for some tenants as they can see they're getting something for their efforts.
There are potentially a lot of problems.
Obviously, if you're reliant on benefits you probably don't have much wriggle room financially and if there's an interest rate rise, fairly good odds you're stuffed and the social housing system really isn't and can't be set up to accommodate a higher number of evictions.
I'm also thinking that this is going to be absolutely slaughtered fraud wise especially in areas like London where house prices move so quickly. Use other peoples money to buy an asset you can later sell for a potentially whacking profit? No incentive for shenanigans there.
Also are you going to ensure low income/no benefit families are given the same opportunity to buy? I'd be well hacked off if I'm stuck renting whilst Billy and Betty Benefit down the road are happily buying their own house.
It's been a while so I'm not 100% on the current regulations but is it still possible to get Guaranteed pension credit then sell your house without falling foul of the capital rules?