The Guardian launches its Christmas appeal on Saturday. This year it is on behalf of charities that support destitute people who are seeking asylum, and the young homeless. The reasons for their plight are often complex but the headline explanation is simple: social housing is scarce and getting scarcer; rents in the private sector are rising; and housing benefit is falling.

On Friday the specialist journal Inside Housing published research that showed a new and significant factor behind the sharp rise in the numbers relying on emergency support. The right to buy, first introduced in 1980, already abandoned in Scotland and soon in Wales, was successfully reinvigorated in England by David Cameron five years ago. It has been a boon to the buy-to-let market and a curse on councils that find themselves renting them back at hugely inflated cost. Soaring house values have turned what should be a place to live into a golden asset. Former council properties have been snapped up by private landlords. In the most prosperous areas, up to 70% of former council homes are now privately let. Private rents out of London average over £200 a week while council rents are nearer £90 a week.

Councils in England have been sending up emergency flares for more than a year, trying to alert the government to their inability to build enough new homes to replace the ones they have been forced to sell, with predictable consequences. In the last five years, since right-to-buy discounts were nearly doubled, 54,581 homes were sold and only 12,472 homes were started. Some are built in one authority from receipts of sales in another, compounding local shortages. Councils have to use part of the receipts from sales to pay off housing debt, and can only keep a third for replacement. They are still banned from borrowing to make up the full cost of buying or building new ones. Between now and 2020, councils also face having to sell off higher-value council homes in order to fund discounts on housing association homes that are due to come in under right-to-buy provisions.

Like so much else that has happened since 2010, social housing policy has not just been damaging but contradictory, fostering the chimera of a property-owning democracy in an age of shrinking social housing stock and rapidly growing demand. The government makes bold promises on new affordable homes to buy. But what’s needed is homes that people can afford to rent.