There’s a building site on the corner of Princess Street and Canal Street in Manchester, a pit of rubble surrounded by hoardings advertising luxury living in the most obnoxious ostentation. It’s hardly an isolated development; gentrification is the new urbanisation, with the rich building themselves fashionable new pads all over our city spaces. As for the country, whole villages are being killed as houses are bought off as second homes until there are too few full time residents to support any kind of economy.

At the same time, we’re living through something of a housing crisis. Monbiot, though it pains his environmentalist heart to say so, reckons we need another three million homes building in the next decade and a half, and points at some examples of truly compelling need:

Wendy Castle moved into her flat in the Trellick Tower in west London when her eldest child was a baby. He’s now 16, and she has three others between 13 and 2. But her flat has only two bedrooms. She sleeps in one of them with her two youngest children. The room is completely filled by beds. On one side they are jammed against the window, which no longer shuts properly. On the other they are pressed against the heater, which can’t be used because of the fire risk. Her two oldest boys share an even smaller room.

She keeps her flat in a state of Japanese minimalism, but in the tiny living room the children were sitting on each other’s laps to watch the television. Like all the women I met that day, Wendy – tough as she has become – cried when she told me how this crowding was affecting her children. Her oldest boy is falling behind at school because “he physically does not have space to do his homework. He can’t do anything till the other kids go to bed.”

But the real shock came when she explained why she was stuck. Kensington and Chelsea, like several London boroughs, operates a points system, reflecting people’s level of deprivation. Every Monday morning it posts up the flats available for social tenants (those who pay less than the market rate). People with enough points can bid for them. Wendy has 40. She has been able to bid on only one occasion. Though her family is officially “severely overcrowded”, she came 87th out of 92. Eighty-six households, bidding for the same flat, were deemed to be in greater need than hers. “I’ve tried everything. But when I ring them they say ‘I don’t know why you bother – you ain’t got the points’.”

There are others, and this anecdotal evidence seems consistent with what I hear too. One of my flatmates, whom my anti-Southerner prejudice had led me to think of as pretty posh, recently told me he’d never had his own room, and had always slept on a mattress in the lounge. It certainly seems to be no exaggeration to talk in terms of “crisis“.

Using figures from the government and the housing charity Shelter, Monbiot summarises: “Over half a million households are officially overcrowded, 85,000 are in temporary accomodation, 1.6m are on the social housing waiting list”, and that’s without counting the people on the streets. Clearly, all these people need somewhere to live; the question is where?

Shortly after it came to power in 1997, the Labour government provided its own answer to that question, designating some parts of the country as “Greenbelt” – pristine rural paradise to be preserved at all cost – and “Brownbelt” – a term more associated with urban decay, indicating the old rubbish that anyone can build on. However, Brownbelt covers a lot more than most people realise: in particular, it covers a lot of people’s gardens.

No count is being kept of how much garden space is being lost to urban regeneration, but it is a lot and, while I’m always happier to see space shared than kept as private property, we shouldn’t neglect the importance of even private greenery in the city, keeping our air clean and, by retaining water, dramatically reducing the risk of flood and drought. Things are made worse by people’s urge to turn gardens into miniature car-parks, and the Olympics – that time-honoured vehicle for merciless gentrification – look set to trample over more than a few allotment gardens.

Given the underestimated environmental value of the Brownbelt, some – including respected environmentalist Sir Jonathon Porritt (though, personally, I have a little difficulty respecting anyone whose name is prefixed by “Sir” or “Dame” or what-have-you, he does seem to be kosher) – are calling for a complete rethink on the subject of the Greenbelt. Since many of the objections can be dismissed as selfish NIMBYism, it seems fair enough, maybe we do need to start building more houses in the countryside.

A word of caution is in order here, though, too. While a careful choice of sites may limit the environmental cost of what we bulldoze, we also need to think about the environmental overhead of what we build. Suburbia – especially as the term is used in the U.S.A. – is an incredibly inefficient place to live. In terms of space management, energy use, and especially transport, it’s wasteful on a scale that, until the twentieth century, was unknown to all but the most decadent of monarchs. It’s even being suggested, quite plausibly, that the suburbs may have to be abandoned, or at least completely rethought, as a result of ‘Peak Oil’.

However, this idea of mass building to arrive at affordable housing rests on a fairly narrow definition of “affordable”. Money is a human invention; we should be controlling it, rather than letting it control us. During a housing crisis, can we afford to let 676,000 homes stand empty? Can we afford 260,000 second homes when we need another 500,000 first homes? I say we ban them, pure and simple, or maybe think about a housing tax structure that would see tax proportional to the area:inhabitants ratio (ie, the emptier the property, the more it costs). Monbiot also suggests helping older people move to smaller flats; it’s a good idea, but these are temporary measures at best.

The invisible hand of the market is very visible here, and it’s pushing us to places we don’t want to go. Sure, the bubble of speculative property development is in the middle of bursting, so the price of owning a house should fall in line with the price of renting a house, but that’s still a lot of money; more than most of us can afford. Sub-prime lending kept the market ticking along for a while, but surprised no-one by proving fatally unstable. And, increasingly, the invisible hand is pushing us to make a choice: mass homelessness and overcrowding, or else the paving over of half the country; social disaster or environmental disaster. Might it not be better – might it not be more affordable – just to chop off the invisible hand?

What this country needs is socialised housing.