The green, green fields of home are under threat: from houses, houses and yet more houses

Before the eco-warriors dismantle their tree camps from which they fought such a feisty anti-road campaign, they should look carefully at the land below. It is houses as much as cars which now threaten to destroy the green fields of England.

A new study published this week by the Joseph Rowntree Foundation warns that London, Manchester and the Home Counties face an acute housing shortage due to a larger than expected growth in the numbers of households in these regions. New Government figures suggest household numbers up to the year 2011 have been underestimated by 26 per cent - meaning 737,000 more households. House prices and rents will rise, it says, unless building levels increase to match this new need. The phrase "new town" is being mentioned for the first time in a decade.

This news is likely to be greeted with as much euphoria as alarm. There will be cheers resounding through all those hundreds of thousands of houses blighted by negative equity. Builders will be throwing up their hard hats at the prospect of customers queuing at the door. The Government will be comforted by the thought of voters in its south-east heartland feeling prosperous once more thanks to the housing market.

However, local planners in the affected areas may not be so happy. Surrey has almost run out of open land that is neither Green Belt nor in a designated Area of Outstanding Beauty. Yet demand for property is predicted to rise by 20 per cent in the next 20 years.

Berkshire is in a similar position. Household numbers are predicted to grow by 25 per cent - an extra 80,000 homes - half of which will have to be accommodated on green field sites. An average develoment takes 12 houses per acre. That means Berkshire consigning 3,300 one- acre fields to bricks and mortar.

But hang on a minute, you say. There are already thousands of unsold homes on the market, prices are at best stagnant and at worst falling, and first-time buyers are stubbornly resistant to the lures of owner occupation. Can anyone seriously be suggesting that we concrete over the precious few remaining green fields in south-east England and Manchester just in case a boom looms on the horizon?

The Rowntree researchers accept there is a paradox. The authors of the report are Steve Wilcox and Alan Holmans, the former chief housing economist at the Department of the Environment. These are men who know their sums. "There is a mismatch between the current state of the market and the projections," Steve Wilcox admits, "but in certain regions the market is going to turn around more rapidly than in others."

To a certain extent this is already happening. London and the Home Counties have seen house price rises of up to 20 per cent in the past two to three years, while the rest of the country has stagnated. Many of the more up- market developments in the region are still selling fast, with buyers reserving properties before they have been built.

Rents have also risen, particularly in the capital, as a result of increased demand from young professionals. It is now more expensive to rent a flat in London than to buy one.

The Rowntree report believes this structural change from owning to renting among twenty-somethings has reached a plateau. It coincided with the fall in the birth rate and followed a period in the 1980s when owner occupation had been brought forward by the boom, resulting in a real hole in the market for smaller properties this decade and long-term negative equity. They believe those renters are now at an age where they will opt for owner- occupation, increasing the numbers of first-time buyers in areas where the rental sector will remain strong.

They explain that as many as 50,000 of the extra households will be immigrants from the European Union and English people returning from overseas. Many of them will be coming here for city-based jobs, again increasing pressure on housing stock in urban areas.

But the greatest additional requirement for housing will be in the rented sector, particularly the social rented sector. With new limits on the definition of homelessness and dimishing levels of cash being given to the Housing Corporation, this is unlikely to be met by the housing associations. Instead of increased provision, the Rowntree authors expect to see higher levels of over-crowding and a rise in real homelessness.

What, then, is to be done? The authors offer little hope to the generation ruined by negative equity. They expect their small flats to switch gradually from the private to the rented sector by the crude and painful mechanism of repossession.

However, Steve Wilcox thinks the Government should act on two other fronts: it should encourage housing associations to renovate old properties currently in owner-occupation, saving a few fields and releasing some trapped owners while providing some new homes. In addition, it should take a stronger overview of planning in the private sector. If Surrey, Cheshire and Berkshire are too full or too expensive then families will move out to cheaper counties. This means increasing the planning requirement in areas like East Anglia or Lancashire to allow for outward migration.

Others might argue that market forces will take care of that. If people cannot afford to live in Berkshire they will try Wiltshire or Oxfordshire. If there are enough of them, the builders will start building on the land they are currently holding in reserve and the cycle of recovery will be in full swing.

At the moment there is no sign of that. To take Berkshire, the rate of housing starts in the county has fallen from a high of 6,000 in the early to mid 1980s to around 2,300 a year. The Rowntree report would require a level of around 4,000 starts a year.

On the housing estates which already sprawl across the east of the county For Sale notices are flourishing. Lower Earley, south of Reading, is one of the largest suburban housing developments of the 1980s. The district is served by five estate agents - it was six until last year - and even the most successful is struggling. They can offer you anything from a one-bedroom flat to a four-bedroom detached house. The only shortage is a shortage of buyers. The only houses currently in short supply in Berkshire are period properties in quaint locations. More new housing will do nothing to ease that.

If you stop on top of Junction 11 of the M4 and look north to Lower Earley you see row upon row of tiny modern roof-tops, the 1980's equivalent of a Coronation Street landscape. If you turn south you see fields with a few cows. At least, you do now. This is the land which would be earmarked for bricks and mortar. If there are no takers in Lower Earley, will they really find the buyers for a few thousand more new homes across the road?