About 3.5 million people - about 6 per cent of the population - are members of the National Trust, an organisation passionately committed to the preservation of Britain's coastline, countryside and historic houses. Thanks, in part, to its lobbying, better legislation and imaginative conservation, the future of most historic buildings is secure. That cannot be said for the coast or the countryside, especially in areas of rapid population growth such as the South East. As Sir William Proby, the trust's chairman, said yesterday, more than 10,000 acres of green belt are at risk from development in regional plans. Since 1995, more than three square miles have been lost to development each year. A country with some of the finest landscape in the world is in danger of losing oases of beauty and calm that have historically refreshed and inspired its people.

The reason is that the land is needed for housing. There is a critical shortage of accommodation in the more prosperous parts of Britain, one that is driving up prices inexorably, skewing development, widening social disparities and leading to critical shortages of workers. As smaller family units, migration and prosperity increase the demand for more and differently configured dwellings, the Government estimates a need for at least three million new homes. This is a direct challenge to the National Trust, the Campaign to Protect Rural England and all those who oppose further encroachments on open spaces. The conflict is as debilitating as it is pointless. It has led to bitter arguments between Whitehall and councils in target housing areas. It has prompted accusations that conservationists are pandering to Nimbyism, blocking economic progress and trying to turn back the tide of development.

There need be no conflict. The culprits are the planners, architects and bureaucrats, who insist on building the wrong kind of housing. The baleful architecture of the 60s and 70s has not only halted further construction of the hated tower blocks; it has also ensured that no one is now ready to contemplate any high-rise schemes. This is absurd. If ribbon development was the bane of the 30s, the housing favoured today is little better: sprawling estates of identical boxes with pocket handkerchief gardens, faux Georgian mansions, occasional pastiches of Victorian terraces. This is wasteful of land. The Government says 60 per cent of new housing should be on brownfield sites. The target is too low. The National Trust's call for 80 per cent is fully achievable - but only if builders are ready to go up instead of out.

Scandinavia, for years, has achieved high density and environmental economy, as well as a sense of community, by building blocks of about eight storeys, tight enough to foster a community and well interspersed with open space. Architectural ratios of light, space and distance mean that these can house as many people in the area as isolated tower blocks. Could not the same be done in any dormitory town in the crowded South East? High Wycombe is notoriously long, low and sprawling: medium-rise developments would create a more concentrated, livelier centre. The same is true anywhere - Acton, Plymouth or Solihull. The trust is right to focus on the importance of green spaces. Good, imaginative architecture should combine space, density and community, and environmental awareness. Only then will our heritage be saved.