On Saturday on BBC2, Peter Brook revisits his film of `Lord of the Flies' and finds out what happened to his boy actors. But there is a much more pertinent question: what does the book mean to us now?
If Lord of the Flies was a person it would be just about ready for a mid-life crisis. Forty-two years old now, still steadily prosperous but mostly getting by on teaching jobs these days, trading on its exemplary didacticism and its youthful fame. The conceit is prompted by a film to be shown this Saturday on BBC2, a documentary in which the director Peter Brook returns to the location of his film of the book, accompanied by some of the boys who acted in it. They are not boys any more, naturally, which raises a pertinent question of identity - are these grown men really the same people as the children who made the film 35 years ago? Brook is interested in whether their brief expedition into savagery shaped their subsequent lives and, if so, exactly how.

What did they learn from their intimate encounter with a story that has been so influential in our attitudes to children, from acting out the rituals that most of us only observed at a fictional distance? More importantly, perhaps, how has their subsequent experience changed them? But, if people grow old and learn new things, so too do books, with this important distinction - their consciousness is that of their continuing readers. So what kind of life is Lord of the Flies leading now?

It is a fairly presumptuous question, if only because it isn't a simple thing to say what sort of life Lord of the Flies led back then. That it was a prodigious success isn't in doubt - it found an immense readership, and it did it in an interesting way. Although it received more than respectful reviews in this country, it was its American reception that transformed it from a critical success into a cult. And there is a kind of mystery here. It isn't enough to explain the extraordinary success of books by looking only at their intrinsic qualities - you have to ask questions about their luck too, about the way in which they coincide with a hitherto unperceived appetite, an absence which the presence of the book suddenly makes conspicuous.

What was it that young American readers needed (the book was a campus success above all) and that this novel supplied in such rich measure? It isn't immediately clear why a generation for which the horrors of Auschwitz and the Second World War were still fresh should seek out a moral fable so unblinking about people's capacity for evil. It couldn't possibly have a consolatory force, unless it was the severe consolation of clear sight. The theme of the book, Golding later offered, was "grief ... grief, grief, grief" - so it must have offered too the satisfaction of a beautiful funeral service for dead ideals. On the beach, dazed by the magical resurrection of peace and safety, Ralph cries for the first time, cries "for the end of innocence, the darkness of man's heart, and the fall through the air of the true, wise friend called Piggy." If the story has black borders it is because millions of deaths went into its making.

But had it been published just 10 years later its history would surely have been very different. After all, the conditions Golding creates for his social experiment could serve as a blueprint for the manifestos of the late Sixties - no superior authority, no curb on instincts, no duties imposed from above. Golding took the imaginary paradise of children's books (Ballantyne's Coral Island is named twice in the book, by the boys themselves and by the immaculate, impercipient officer who rescues them from their "fun and games") and then applied to it the knowledge he had acquired from his experience as a schoolmaster. The promise of the island is perfectly encapsulated in Ralph's jubilant cry on finding that they are entirely alone: "No grown-ups!", he exclaims, in "the delight of a realised ambition". But Golding's novel shows exactly what can follow from realising such ambitions. It's true that the children of the Sixties could read the novel without ever seeing themselves - they would see the corruptions of power and violence, even, God knows, glimpse the military- industrial complex in there somewhere. But could they have read it so blithely if it had not already achieved its status as a classic? How many readers in 1968 would have identified with Ralph's pleading assertion that "the rules are the only thing we've got" rather than Jack's hedonistic cry of revolution: "Bollocks to the rules"?

Golding did not invent the cruelty of children as a fictional device - there is a Saki story called "Sredni Vashtar" in which a malevolent young child prays devoutly for the killing of his mother and relishes the death when it comes. But that was a unique child, safely contained within the conventions of Gothic horror. Golding's shocking innovation was to take ordinary children and produce a similar atrocity. The island - artificially benign itself - is a petri-dish in which something terrible is cultured out of something harmless, by the simple process of neglect.

These days, of course, the experiment is less neatly contained. Who needs a desert island to prove these dark theories? It can be replicated on a run-down housing estate, or a shopping mall, or a suburban verge on which two girls kick another to death, spurred on by precisely the heedless tribal violence Golding described. Indeed, he became a kind of unwilling expert on such dislocations. When James Bulger was murdered in a game gone bad The Daily Mail asked Golding to comment - presumably because he was thought to have a pre-emptive claim on juvenile savagery. Tellingly he turned away from notions of elemental evil, concentrating instead on the "conditions in which cruelty seems to flourish". The link he made with Lord of the Flies was not the deeds of children but the withdrawal of adults. In this sense his book has evolved from grave allegory into a sombre kind of social realism. What was printed as retrospection - a reflection on decades in which civilisation had worn thin - has come to seem premonitory. We can no longer be as surprised by what it has to say, not only because it exists as a cultural entity even for those who have never read it, but also because life has horribly exceeded its art.

Ever since it was first published Lord of the Flies has been seen as an "instructive" work - so it is maybe not surprising that it has, for all its secure status as literature, become a children's book - prescribed in schools in the belief, perhaps, that it will alert them to their own awful potentialities. But maybe, 42 years on, it is in the wrong job. Looking at it today, you are struck most of all by what isn't there, an absence perceived in all the children's literature that preceded it as a joyful liberation. If Lord of the Flies should be a set-text for anybody these days, it should be a set-text for the grown-ups who have gone missingn