Britain's housing crisis can scarcely be exaggerated. We need between 90 - 120,000 new affordable homes every year, yet only 30 - 40,000 are being built. This means that more and more of the population will be homeless or underhoused.

The government says that 50 per cent of new housing should be on derelict urban sites. But this isn't a target, just a reflection of the status quo - the figure is currently 47 per cent. House-builders are concentrating instead on the countryside , causing both environmental destruction and social dislocation. People who need affordable housing will be forced to commute to work, shops and services.

As well as affordable homes in the cities, we desperately need community projects and new green spaces, to provide a sense that the neighbourhood belongs to us and that we belong to the neighbourhood. A recent survey for Barclays Site Savers by psychologist Dr David Lewis found that only 23 per cent of 15 - 24 year olds feel a sense of local belonging, while only 27 per cent believe there is a good community spirit in their area. He linked this to two things:

1. derelict land, which is:

"seen to create and compound a sense of alienation, cynicism, a lack of confidence, indifference and distrust within communities"

"the feeling of inability to change one's surroundings" .

These developments fragment community, destroy jobs and depend heavily on cars. The day we see developers building "inclusive developments" will be the day that direct actions like this cease to be necessary.

The problem results from planning and land use policies which seem designed to help only the developers, rather than those in need of benign development. We have the laxest planning regime there's been for thirty years. Local authorities are also finding themselves forced to sell their vacant land to whoever comes along.

Developers have little interest in building low-cost homes in cities or in getting involved in community projects, because these don't give them much return on site prices of up to £500,000 an acre.

The government seems to have forgotten the commitment it made in signing Agenda 21, to:

"support the shelter efforts of the urban and rural poor, the unemployed and the no-income group, by adopting and/or adapting existing codes and regulations, to facilitate their access to land, finance and low-cost building materials".

Organizations such as the Groundwork Trust and the quango English Partnerships are overseeing some good projects, but these are a drop in the ocean. In the absence of meaningful initiatives from government, local authorities and business, it is left to activists to do what these sectors have neglected. We have an excellent precedent to guide us.

At the end of the second world war, Britain confronted a situation uncannily similar to that of 1996. The cities had been blasted out - not by demolition contractors but by bombs. As the service men returned home, the rate of both household formation and homelessness soared. Seeing that the government would do little for them, the under-housed of Britain decided to sort out the situation for themselves.

On May 8th 1946, exactly 50 years ago, the biggest squat in British history began. In over a 1000 places around the country, people occupied derelict army camps, bombsites and empty buildings. They rebuilt their communities to their own specifications. Their actions led to changes in government policy, and housed thousands of families who would otherwise have remained homeless.

Like them, we've come to see that there's no substitute for action. No one else is going to rebuild our broken cities, our broken communities and broken society, so we must do it for ourselves.

What we need is some physical and political space.
This means:

• New planning guidelines which leave developers in no doubt that urban sites are for low-cost housing and community projects rather than the more lucrative superstores, office blocks, multiplexes or high-cost housing. This would bring the inflated price of derelict land down to realistic levels, and dampen the speculative market.
• Far bolder targets for derelict landuse - 80 or 830 would make more sense.
• Banning the legalised bribery called "off-site planning gain", which helps developers to push through unpopular projects.