However, if you are disabled, ill, or just unemployed the government offer you something pathetic like £60 a week towards your rent and about the same to live on. If you live somewhere that costs more, like anywhere out side of a council provided house, the might pay you a bit more, but if you a single living in a 2 bed apartment, they will "tax" you for the unused room.
The lack of affordable homes for the poor is an issue that goes someway to causing homelessness and definately provides a way for rich landlords to syphon money out of the welfare state.
The issues are that a second home (or renting out your original apartment) when you upgrade, results in you the landlord paying two mortgages. So the mortgage for your apartment might still be £400 a month, to cover maintenance, rates and make a profit you need to charge £800 a month. Putting that out of many people's markets.
But that isn't the worst. Say the government do build 100,000 affordable homes costing £100-£150k to own. The property tycoons are straight in there and buy the majority of them off plan. By the time they are ready to live in, rather than a lower class family being about to get a £400 month mortgage on one of the, the tycoons are renting them out for £800 and sitting on a beach somewhere. Worse, in a lot of cases they will chop the house up into 2 apartments and rent each out for £600 a month.
This already happened. Most of the council housing stock was allowed to be sold to private owners in the 80s/90s. I can go onto a local rag here and find properties which were council houses with £60 a week rent being rented for £700 a month.
*Prices dependant on the area you live, for London, add a 0