The problem comes down to high house prices. Because when the house prices are high, rents are high, because a landlord needs to make a return on his investment. Hence the disparity between what someone in social housing can pay, and what a market rate would be.
Unfortunately I don't know what the solution is. We cannot afford to move, because we live in a high house-price area (outside of London). If we were simply to move into an identical house to our's, we would have to pay 10s of thousands of pounds in TAX, even before estate agent's fees, solicitor's fees, removal costs etc. To up-size therefore would be costing us about £50k even before we've added on the extra value of the new house.
That's not a good situation for the market to be in, where relatively well-off families are stuck. We didn't ask for the house prices to go stupid (they weren't when we bought this house), and we can't realise the value of the house.
But you can't artificially lower house prices, because of the problem of people who bought at a high price.
The only solution in my eyes is to build council and state owned housing in EVERY postcode, so that all areas have housing available which is out of the market place. But that is a huge investment, and building plots sell at a premium. But in my eyes that would be an investment worth making, would shore up the construction sector and would reduce benefits pay-outs in the long term. But the Tory government won't go for it, they prefer the market to lead the way. But until you take social housing out of the market place, this problem of people living in 'too valuable' houses will keep on recurring.