A FEW years ago a critic of the National Trust called it "a kind of holding company of the nation's dead past". The phrase sticks because it contains a grain of truth - or perhaps more than a grain.

The dustsheets that climax an end-of-season event popular at many trust properties - the tweely-named Putting the House to Bed - could just as appropriately be shrouds. Living houses don't go to sleep.

Nor do most routinely shut out the sun, denying visitors the chance to see rooms as their creators would enjoy them.

Then there is the trust's preoccupation with historical purity. At Studley Royal, the renewed yew hedges remain untrimmed until they reach the above-eyeline level at which they were clipped in John Aislaby's original scheme. The result is a loss of attractive views of the water gardens - for instance, from the path near the stepping stones above the lake.

OK - Aislabie's idea was to create sudden, mouthwatering vistas at specially-chosen points where the hedge was lowered or cut through. But in repairing his neglected masterpiece, might it not just be possible to improve on the original here and there?

But if too slavish to "the past", the National Trust must be doing something right. In fact, something very right. For it has just signed up its three millionth member - a Midlands computer consultant. Enrolling himself, his wife and sons on a family ticket he actually took the trust's membership to 3,000,004.

By far the biggest national conservation organisation not only in Britain but Europe, the trust now has more members than the population of Wales or, perhaps more strikingly, of, Nottinghamshire, Derbyshire and Leicestershire.

But what especially commands attention is the pattern of growth. It took the trust 75 years - from its inception in 1895 to 1970 - to gain a membership of 200,000. But in just a little over the next ten years, the total multiplied five times to one million.

In less than a decade, from May 1981 to October 1990, the number then doubled to two million. And now a further million has been added. What is the secret of this extraordinary growth?.

Of course the trust, despite its museum tendency, has great achievements to its credit. Enterprise Neptune has saved 600 miles of often hard-pressed coast. Many of the trust's houses simply would not have survived outside the trust's care. And the trust's conservation-minded farming, once regarded as at best irrelevant and at worst reactionary, is increasingly being looked at as a blueprint, or rather greenprint, for the future.

Not least, the trust is user friendly. On its countryside properties, its welcome extends to creating new paths, like the links between the Cleveland Way at Robin Hood's Bay and the old coastal railway line. Trust notices are pleasingly designed, with off-limit areas gently signalled.

Trust tearooms serve decent food in agreeable, even comforting, surroundings. And the trust works hard to provide each of its admission-charging properties with a lively programme of events - vital against ever-increasing competition for people's leisure time.

But is this enough fully to account for the staggering rise in trust membership?

PERHAPS it is not chance that the explosive growth coincides with a period of deregulation, a general slackening of controls in the interest of stimulating enterprise and creating wealth and jobs. While this might have brought economic benefits, it has also quickened what the architect Clough Williams-Ellis, in his 1928 book England and the Octopus, an early attack on sprawl, called "the mess rate".

In the Britain of the late twentieth century and early twenty-first century, its characteristic face is the landscape of out-of-town retail parks, hi-tech business parks, and still-advancing housing that one seems to see almost everywhere.

In a contribution to a timely new book, Simon Jenkins, former editor of The Times, tells how, travelling round England to research his own recent book on parish churches, he found people everywhere apologising for some horror inflicted on their neighbourhood. It might be a line of pylons, a big-shed industrial estate, a wind farm - but the feeling of dismay was universal.

Research by the Council for the Protection of Rural England shows that between 1980 and 2000 - the exact period of the National Trust's sudden vast growth - a greater percentage of open land was lost to development than in any other period of the twentieth century.

Against this relentless encroachment, the dramatically rising membership of the National Trust seems almost a flight to the beauty of unspoiled places, and a desperate, or perhaps one should say deep-down desire to hold on to our links with the natural world and our historical roots.

With membership of comparable organisations also rising fast - the RSPB now has more than a million members, and membership of county wildlife trusts has doubled since 1995 - what we are witnessing is a reaction against the ugliness and degradation that threatens to fulfil Philip Larkin's prediction, made in 1975, of Britain as the "first slum of Europe".

The virtual butchering of the Vale of York by the new Teesside-Shipton power line is an outstanding example.

Will the politicians take any notice? Will they pick up the message that people want better care for Britain's fast-diminishing countryside? Almost certainly not.

And yet there is an overwhelming reason why they should. The National Trust's membership alone exceeds that of all Britain's political parties put together.

That must be telling us something.

* Remaking The Landscape: The Changing Face of Britain, edited by Jennifer Jenkins (Profile Books £20)