Like thunder clouds massing on the horizon, the threat of vast new building programmes looms black over the rural landscape. It was entirely characteristic of our present planning chaos that, while the leaders of our three main political parties were writing in unison to The Times last week to advocate "the protection of our countryside in its rich personality and character", the Department of the Environment was trumpeting the need for 27 brand-new towns.

Is there any real need for 27 new towns? The answer is obviously, "No". The population is not increasing that fast. Yet how can anyone stop the the juggernaut of government bureaucracy grinding forward without regard to the wishes or real needs of ordinary people?

The problem is easier to grasp if one small part of it is considered in detail. In Gloucestershire, we are told that the county must find room for 53,000 new houses by the year 2011. The threat is not merely that existing villages will be expanded into towns, but that new settlements of at least 7,000 houses will be built. The area most at risk is the Severn Vale, the flat ground on either side of the river.

And why are so many houses thought to be needed? Simply because the planners have trawled through the figures for the years 1971 to 1993, projected forward the trends they have discerned, and come up with that number.

There is every indication that the figures are seriously flawed. Much depends, for instance, on migration into the county. In the 22-year survey period, gain by immigration averaged 2,700 persons per year, and this number has been projected forward to the year 2011. Yet private studies have shown that in the five years 1988-93 the average gain was not much over half that.

Of course, there are many factors, far more immediate than population increase or movement, which keep the bandwagon of house-construction rolling. One is the greed of developers; another, the desperate financial straits in which councils find themselves. Only last month it was revealed that Michael Honey - Chief Executive of the Gloucestershire County Council - had been preparing to sell 670 acres of council farm land to J S Bloor, of Derbyshire, as a site for 6,000 houses, in a deal worth pounds 55 million. For the time being that little idea has been squashed, and the County Council's farming committee has agreed that no negotiations should take place until the structure plan has been finalised.

All the same, communities in the Vale grow increasingly nervous, and several local movements have started up - Don't Destroy Standish, Keep Eastington Rural - designed to protect particular villages. There is also one body of a different kind - the Gloucestershire Structure Plan Appraisal Group, or GSPAG - which operates from Nupend, a hamlet near Stroud, and has brought together representatives of many threatened parishes in an attempt to fight the whole building policy, rather than to safeguard individual sites.

At a cost of pounds 1,400 the group commissioned two reports from John Allinson, Senior Lecturer in Town and Country Planning at the University of the West of England, Bristol. His careful analysis predicts that net immigration into Gloucestershire from now until 2011 will average 1,600 persons a year, rather than the 2,700 forecast by the council.

According to John Darwent, Treasurer of GSPAG, the trouble is that such facts bounce off the planners like peas off elephants. "We keep coming up against this closed-mind attitude," he says. "The planners don't seem to care about actual numbers. All they want is to bulldoze their ideas through meetings."

He points out that any decision to build a new settlement is irreversible: once construction has started, that stretch of land has gone under bricks, concrete and asphalt for ever. In his view, and that of his group, the County Council simply does not have the hard evidence to warrant an assault on the environment on the scale which it is proposing.

People who live in villages, and try to defend their patches, are inevitably accused of nimbyism. But if they do not stand up for themselves, and make the planners see that they are destroying their own main, irreplaceable asset, there will soon be no point in anyone migrating to the country - because what was once a green and pleasant landscape will no longer be any different from the town.