isthisunreasonable - Good Luck. I wish you the best for your exchange and your new home. I hope the move will be happy for all involved, and thank you for an interesting debate. 
I think the flaws are so many, and the issues involved so complex that it is really difficult to get ones head around all the consequences of the various changes involved.
In the last 5 years I have been a home owner, I have been a landlord, and I have been a tenant in a private rental. Neither is a bed of roses.
When you consider the high house prices (extortionate in some areas), the high mortgage rates many are stuck with, and the difficulties in getting mortgages for "normal folks" right now, it is easy to see how private rent is so high.
In order to make any profit on rent, landlords need to either have a very small mortgage or paid a deposit of more than 50% of the house value. Without the profit, there is no incentive to be a landlord, no value in it, only hard work, and lots of accounting. I reckon there is also a group of landlords who are letting property they have inherited, so no mortgage involved, just profit. For landlords such as myself, there was no profit involved, only hard work, the bonus to us was that we did not have to sell our house whilst overseas.
When you consider that most landlords are either small time home owners like myself, people with a second home, or large developers, you can see that the biggest culprit in the private rental market are the developers and to a certain degree those with a second home, together with the banks. The combination of mortgage rates, high house prices, and profit driven developers/landlords, make it very difficult for normal people to either buy property or rent privately.
This creates an enormous gap in some areas between the rent you pay as a private tenant and one in social housing. How can this gap be closed?
Force house prices down?
Introduce Rent Bands that landlords need to stick to?
If private rent came down to an acceptable level that social housing would perhaps be no more than an insurance that people who need a home get one, and for as long as they want, rather than just cheaper than market value. Maybe it is utopia, but my idea is that social housing should be a temporary measure until you get on your feet, however long that takes.
Less people would need social housing if rents were affordable. I dont think that the solution is to build more social housing, this is not decreasing the gap between "the rich" and "the poor".
I think in order to make these changes the rich has to become less rich. (I know, flame me. Now all sections of MN will hate me, not only those in social housing!
)The wealthy need to "fund" these changes, through higher taxation, higher tax on bonuses (or even less bonuses - maybe the banks can pool some bonuses back to their customers!) "wealth tax" on second homes and luxury cars. Higher Vat rate on Luxury holidays and alcohol! Only by making the rich less wealthy will the poor become less poor.
Cameron says "we are in this together" We are, but only to the extent that the wealthy need the poor to increase their wealth, we need it to be the other way around.
Bear in mind that I came from a society where 75% of people are middle class and home owners, where there is very little social housing, but which is means tested and temporary, and I have seen how well this works. But it can only work in a society where house prices dont vary so much, and where house prices are pretty stable and not extortionate. And where there are enough jobs, jobs that pay well, and banks are keen to lend at decent mortgage rates.
Well, I have rambled on enough with my Utopian dreams. Enough already.