Britain's green belt is 50 years old this week. Postwar prosperity meant there was a big demand for new housing, so the planners, in their infinite wisdom, decided to stop it. Rings were drawn on the map around our towns and cities, and within those 'green belts' no development was allowed, except by special and exceptional dispensation. Urban sprawl was, apparently, the new enemy.

This policy - like the rest of planning policy - has been a disaster. The reason why property is so expensive to buy or rent (especially in London and the South-East) is precisely because new building is strangled by this collar round our conurbations. That's why houses are becoming unaffordable, why our hotels are so expensive and so poky, why our shops have to charge such high prices, and why the supermarket aisles are so uncomfortably narrow.

Sure, a lot of people get some green fields to look at. Specifically, all those people who have to live miles out of town because they can't afford city rents any more, and who have to take the train every morning through this rustic museum. The trouble is, the green belt has expanded so much and commuters' travel times are now so long that they're usually too tired to look out of the window and enjoy it. Not that there's much to enjoy: all those EU subsidies to the barley barons make most of it look uninvitingly like Kansas anyway.

It's quite feasible to bring the countryside close to people without closing off vast rings of it to development. It's quite possible to develop large parts of the countryside without ruining it. But instead the bureaucrats of 50 years ago left us with the typical heavy-handed bureaucratic solution: draw a circle, stop any development the other side of it, put it back in the file, and don't inquire too deeply about the consequences.