Great libraries, like great forests, take centuries to grow. Both can be destroyed in hours. The great collection of Alexandria was burnt down, that of Dresden bombed, that of Baghdad looted.

It’s not the vandals like Joseph Goebbels — the Nazis’ bookburner-in-chief — who are the worst culprits. It’s the law-abiding customers who do most damage. Public libraries reckon a hardback is good for 150 borrowings or 50 photocopyings before disintegrating. Even rare-book curators, who wear cotton gloves to keep finger-acid off pages, know that every time one of their beloved volumes is consulted its life is shortened. The temperature and humidity comfortable for human beings is disastrous for paper.

All of which makes Google’s initiative to create a giant virtual library good news. As announced last week, the web-search company has entered into an agreement with five of the English-speaking world’s grandest libraries: those of Harvard, Stanford, Oxford, and Michigan universities, and the New York public library.

Of course, any book lover faced with the web rather than ancient shelves will mourn the loss of sensory experience — even the smell of places like Duke Humfrey’s medieval reading room in the Bodleian library at Oxford. But if this initiative comes off it could be the biggest leap forward since Gutenberg moved type.

The aim is to digitise for circulation on the web a vast collection of out-of-copyright items. All the great books of the West will be represented. They will be reproduced as facsimiles but also, it appears, as searchable e-texts.

The Google project far exceeds the current Project Gutenberg e-text library, which has around 13,000 out-of-copyright books on-line for free, but which does not have access to the first editions and rarer texts that Google’s partnership with the libraries will give it.

The first phase will take 10 years,which will make it the fastest, as well as the biggest, library ever assembled. And the online library will ensure the preservation of our civilisation’s great books in two ways. Nothing burns in cyberspace and nothing decays.

With the Google version original copies of treasured volumes can be wrapped and sealed in cool, dry coffins, safe for ever, while eager students gaze via the net at the beautiful illustrations by Dante Gabriel Rossetti of his sister Christina’s poem Goblin Market; or Turner’s pictures featured in the 1834 book Wanderings by the Seine.

There is an added attraction which will have occurred to any teacher. From PlayStation to postgraduate’s Mac, today’s students are web-oriented. Undergraduates see the college library as a kind of cemetery, a place for dead thinking and very old people. They want information instantly and they may well want to drink coffee, smoke, listen to music and talk while they are getting it. The Google library will enable that.

So three cheers for Google and its library partners. But then, of course, comes the uneasy afterthought. Why in hell’s name are they doing it? Why should we expect the biggest, most expensively compiled library in the world to be free? How can Google sell this huge giveaway to its shareholders? Why would Harvard, which charges outsiders $800 a year for reader’s privileges at its Widener library, “give away” material for nothing? How will Harvard explain this generosity to its hard-headed trustees (not to say its undergraduates, paying $30,000 a year in tuition fees)? Ostensibly, Google is undertaking the virtual library project as an adjunct to its Google Print service, which makes excerpts available online of books that are in copyright. The payoff for the user is that the online version is searchable, cut-and-pastable and downloadable. But it’s a delicate balancing act. If Google Print gives away too much, the value of the property offline is undermined. Put simply, why pay £20 in Waterstone’s for what you can download free? There is no such inhibition with out-of-copyright material, which makes up about 90% of a library like the Bodleian. But how will Google recover the cost involved? One way, it says, is by partnership with electronic bookstores (“Buy this book” links to Amazon, for example). The Great Books archive may also stimulate user traffic that will enable Google to charge higher advertising rates.

There is, of course, a more worrying possibility. By the act of converting printed books to digital form Google will be creating a new copyright.

Works in the public domain will effectively be privatised. Whether or not Google chooses to exercise its rights, it and its library partners will be owners of the newly processed property. So the vast reservoir of material in the out-of-copyright public domain will become “proprietary”, or pay-per-view. If we get access, it will be because we are “allowed”, not because we have the right. Great Books will go the way of Test cricket. You don’t pay, you don ’t see.

Google hasn’t said it will do this; but, as far as I can make out, nor has it definitely said it won’t.

This is the second time in a year the question has been asked. Last summer the BBC announced that it was intending to “release” its huge archive of sound and audiovisual material onto the web. It will be, with certain restrictions, able to be freely downloaded, but of course ownership remains with the BBC. So why, in a year in which it is having to make ruthless savings across departments, would the BBC give away this material, worth, potentially, billions? And long-term web users will recall that five years ago all the main broadsheet newspapers gave themselves away free online. That has changed — many now demand subscriptions to access parts of their sites. So, two cheers for Google, but also a question: is this really a free lunch?

John Sutherland is professor of modern English literature at University College London