HOUSING, it is increasingly clear, will probably be one of the hot topics of the 2015 election–at least on the left. This morning, Polly Toynbee, the Guardian’s chief hand-wringer, reports on the creation of new slums in east London. As she says, “Labour and Tory governments neither built nor intervened in a market failure where private developers didn't build despite astronomic price booms”. She even quotes our reporting. The Economist and Ms Toynbee then depart–she thinks that the state should build more; we think that the private market could do better. But the key problem, both agree, is the the shortage of housing.

However, it is increasingly clear that parts of the left seem not to understand that at all. Tom Copley, the Labour Party spokesman for housing in the London Assembly, has created a few headlines this week with a report that claims that 36% of London’s former council homes are now rented privately. "Right to buy", Margaret Thatcher’s great vote-winning policy of allowing council tenants to buy their homes, was “one of the key causes of the current housing crisis”, he says. He makes the point that it is–or at least seems–perverse for the government to pay inflated rents on behalf of welfare-claimants living in homes that were once owned by the state.

This view is common. In the latest London Review of Books, James Meek promises to explain the housing crisis, but in reality disappears onto a fascinating tangent about the history of social housing. Right to buy, he argues, “created an astonishing leak of state money – taxpayers’ money, if you like to think of it that way – into the hands of a rentier class.” Essentially, the government's failing wasn't in letting prices rise indefinitely; rather it was selling its own stock just before they began their ascent.

Yet (except in so far as creating new homeowners created new NIMBYs) blaming right to buy for the housing crisis is absurd. In London at least, if anything, the policy helped to alleviate the problem, by using the housing stock more efficiently. With right to buy, London’s many council tenants–and by the end of the 1970s, a solid majority of inner-Londoners lived in council homes–got an opportunity to do something that was very difficult to do in the council system: move.

Large numbers of people bought their homes and immediately sold up, using the proceeds to buy bigger homes out in the suburbs, or outside of London altogether. Huge numbers of aspirational young families were able to move out of their cramped, crumbling inner-city flats, managed by bureaucratic and often incompetent councils, to places like Milton Keynes. Those homes were then freed up for people who actually wanted to live in them.

And who are those council homes rented to? Well some are rented to benefits claimants–people who perhaps might have got a social home in a previous era–at huge cost to the taxpayer. But an awful lot are rented to people rather like me. Indeed, when I first moved to London I lived in a former council flat in a block on the edge of Victoria Park in east London. For young people moving to London after graduating to work in the media, the creative businesses, the City, politics and much else, ex-council flats have provided plenty of cheap(ish) accommodation in once-neglected bits of the city. Indeed, in the absence of new building, they have perhaps been the main means by which London’s spectacular yuppie migration has been housed.

The reality of life in London now is that it is migratory. Each year, net, around 40,000 people in their 20s move into the city, mostly its inner boroughs, from all over the country. An almost identical number of people in their 30s move out, mostly to the suburbs and exurbs on the edge of the green belt. Remarkably few people spend their entire lives in London. The idea that over half of London’s housing should have been controlled by councils and retained on lifetime tenancies is absurd. Even now, the amount of property owned by councils is arguably too high. Families who would like to leave London and live in more spacious homes elsewhere cannot, because they are tied to a social tenancy, even as young graduates who would like to move south cannot afford to.

That is not to say that right to buy ought to be extended indefinitely. Discounts of 70% or more–now common in London–are not a cost-effective way to privatise valuable state assets. But denouncing council sales as the cause of London’s housing crisis is ridiculous. The real cause is the shortage of homes in general, regardless of who they are built by. That is what drives up rents and so puts pressure on the welfare bill. The real scandal is that just as the state divested itself of its housing stock, it also strangled building, and so engineered to increase its value indefinitely.