Let's get one thing straight: Britain is going to build on its green belts.
Over the next 15 years, government projections suggest, London and the surrounding counties need to build around 1.8 million extra houses. Brownfield sites could hold perhaps 600,000 of them. And that, incidentally, is if we include flood plains, contaminated land, bits of back garden, the lot.
So – let's just accept that the green belt is up for grabs and ask: which bits of it?
Barney Stringer, a director of regeneration specialist Quod, has decided to help us answer that question. He’s painstakingly mapped every site in London's Metropolitan Green belt that lies within a 10 minute walk of an existing station. He then excluded all areas designated as areas of outstanding natural beauty, ancient woodland, nature reserves, and so on.
What was left, he wrote on his blog this morning, was "nearly 20,000 hectares of accessible green belt in and around London". Around 2,850 of them are within Greater London. Here’s a map.
Now, Stringer himself is at pains to stress that not all of these sites should be developed: the land he’s identified includes a number of valuable local parks, not to mention Epsom Downs race course.
But it also includes golf courses, farmland, and ugly blank spaces that don't really serve any purpose at all. Look at the areas surrounding the Central Line loop, to the north east of London: there is no reason not to build there, except for the fact that we never have. "People struggling to afford adequate housing," Stringer writes, "might quite reasonably feel a sense of moral outrage at the sight of tubes and trains busy serving fields and golf courses".
Surrey, incidentally, has more land covered by golf courses than it does by housing.
Building next to stations will only get you so far, of course. Let's assume, to pluck a figure out of the air, that just a third of the land identified above is suitable for housing. At average outer London population densities of 3,900 people per square kilometre, it could provide homes for another 260,000 people.
That's a lot – but it's nowhere near enough. What’s more, just because an area has a tube station, that doesn't mean it has enough road capacity or schools. If we're really going to fix this mess, we also need to build on brownfield land, and employ 'intensification' strategies (that is, packing more people into our existing urban areas).
But, as Stringer asks in his blog:
"Should accessible land (expensively served by subsidised public transport) be so carefully protected from providing people with much-needed homes? This isn’t a question that can be solved in the abstract... The truth is some land should be protected, some shouldn’t, and we ought to ask ourselves: are the boundaries we’ve drawn (often many decades ago), still exactly correct in every case?"
It’s difficult to see how the answer to that question can be anything but ‘no’. Not all green belt land looks like the North Downs.