Public land ownership in Britain is in crisis. Since the late 1970s, when the government began what has turned into a long-term land privatisation programme, about half of all public land – 2 million hectares in total, or 10% of Britain’s overall land area – has been sold, mainly to private companies.

Local authority and NHS landholdings have been particularly hard hit. Today, local government owns only about 40% as much land as it did four decades ago. The NHS estate has been even more radically depleted, shrinking by around 70%. And the pace of privatisation is accelerating. Both NHS trusts and local authorities are feverishly selling off the few property assets that remain to them as they struggle to make ends meet in the face of swingeing budget cuts imposed by Whitehall.

If the sell-off continues, there could be no public land left by mid-century. The NHS and many councils could be landless long before that.

Does it matter if the public sector is left without land of its own? Clearly, the government thinks not.

The left’s stock response to privatisation has traditionally been to contest or refute the principal logic driving it, which is that assets are utilised more efficiently in private than public hands.

But this criticism misses the mark where land privatisation is concerned. Land is different. The biggest problem with land privatisation is not that the private sector is not necessarily a more efficient landowner and user. It is that when land moves from public to private ownership, some socially important land uses simply disappear. Why? The crux of the matter is what economists call market failure, a situation where the private sector fails to offer something even though there is demand for it, usually because it is not profitable for it to do so.

This is what has happened as British land has been privatised. Various important demands on the land have increasingly gone unmet, because public bodies now lack the land to meet them and private-sector bodies lack the incentive. Here are some examples of things that, bit by bit, are disappearing from national and local maps: free public parks; genuinely affordable housing; entry‑level farm tenancies; state-school playing fields; public space where behaviour is not surveilled and circumscribed; free long-term residential healthcare; and allotments.

Instead, the private sector has used the land it has acquired to provide things that can be made to pay, such as shopping centres, private parks (and car parks), wildlife “experiences”, upmarket – and often gated – housing.

If there is one statistic that epitomises this shift better than any other, it is that, today, golf courses across the UK cover 10 times more land than local authority allotments (for which around 90,000 people are queueing, with some expected to wait as long as 40 years for a plot). This, if you like, is “efficient” private-sector land use in action. The average rental price of an allotment is only around £40 for a whole year. That, if you’re lucky, gets you one round of golf.

What is the answer? One is to simply stop the sell-off. If further public land is to be sold, conditions should be attached to the sale. Rather than selling land and merely hoping that the private sector uses it in socially beneficial ways, public bodies could insist that they do so. And then, of course, seemingly most radically, there is the option of reversing course. The government could buy land back, to use it for those things that the private sector is failing to do. With talk of possibly reforming laws to enable councils to compulsorily purchase land at discounted rates, perhaps this is not such a radical option after all.

• Brett Christophers is author of The New Enclosure: The Appropriation of Public Land in Neoliberal Britain (Verso, £20). To order a copy for 17.60, go to guardianbookshop.com or call 0330 333 6846