It will be old news to you by now, but as I write this review the National Trust is buying an ordinary terraced house in Liverpool where Paul McCartney once lived. They could probably have had the one next door - identical, but without the story line - for half the price.

The National Trust: the Next Hundred Years, according to its editor Howard Newby, is intended to stimulate a "constructive debate about the trust's future direction". The ownership and management of the country houses we all visit with their shops and tearooms and zealous attendants is a tiny part of it all, he reminds us. Conservation, sustainable development, the countryside, archaeology, gardens and the coast all have their chapters, as do buildings. Most of them are written by university eminences. Some essays are better than others, but stimulating is not a bad word to sum it all up; and this is the only National Trust publication I have seen without any pictures.

The National Trust was founded in 1895, and this book uses the centenary as "an excuse to take stock". A century ago, the rotting of old England was already clear to sensitive persons. The country was too successful for its own good and was palpably disappearing under a welter of capitalist rubbish. The introductory essay by David Cannadine - contrarily called "The first hundred years" - describes in incisive detail how this preoccupation altered as successive generations took hold of the trust. Between the first and second periods of war with Germany people perceived that the character of England, not its sense of antiquity, was the thing under threat, and with that came big chunks of land acquisition. After the second world war came the turn of aristocrats, who used the trust to mount a rescue operation on their vanishing legacy, the country houses with their parks and collections. The fourth generation, the current one, is that of an environmentally concerned landlord of the third biggest holding in the country after the Forestry Commission and the Ministry of Defence.

So, 100 years on, ready for the next move, what should the National Trust do with the mixed bag of land and property collected under these subtly different regimes? For my money, the best essay here is that by Keith Clayton on "The coast". It resoundingly epitomises the trust's predicament. The trust has an ambition to own all 2,000 miles of undeveloped coastline (the whole is 3,000 miles), and Clayton does not shrink from stating unpalatable realities - the first of which is that the whole world is constantly changing. Protect one part of the coast, and the destructive power of the sea is displaced to another. By 2095, given the rise in sea level, the shape of England may be different: the trust may lose its holdings to the ocean, as the Greyfriar monks did at Dunwich, way back. Such organisational self-questioning is not so bad: some other conservation groups have clarity like an illness. Clayton points out that the Royal Society for the Protection of Birds, for example, with its single objective of protecting birds is prepared to alter the landscape to that end and to prohibit access to it - both of which things, he rightly says, the National Trust should not do.

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Will the next 100 years see a Balkanisation of different environmental groups, with the National Trust trying to maintain its conventional, don't-rock-the-boat-too-hard position? In his essay on archaeology, Peter Fowler raises the spectre of fox hunting becoming a sort of living archaeology, to be protected because of its significant place in the heritage-which is a bit like the idea that Paul McCartney's father's house is more significant than the one next door. The point of protecting buildings is to save something good from destruction, not to make an exhibition of significant artefacts.

The concluding essay, "The next hundred years", by the editor Newby, is not conclusive. There is an attempt to define the "core issues" but to me it reads like contemporary planning, all parking restrictions and compromises: in other words, plenty of ideas but no vision. Even so, anyone interested in the future of the land, and in England, will find this book a help in clarifying his or her own position, which makes the book a success on its own terms. It may not have the answer, but it has utility.

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Paul Shepheard is researching landscape themes, assisted by a grant from the Graham Foundation for advanced studies in the fine arts.