The one thing you have to say about V.S.Naipaul is that he is unflinchingly honest. It is not a comfortable honesty. It can convert into cruelty, prejudice, scathing criticism and even racism. But nowhere is that honesty more woundingly directed than against himself. What other writer - what other human being - would encourage and sanction a biography which revealed that, in the course of his life, he had mistreated his wife, abused his mistress, frequented prostitutes, insulted his friends, disparaged his fellow writers, descended into depression and paranoia, and been tight-fisted, tortured and tyrannical.

For his enemies - and they are many - the human flaws go so deep that they undermine him, not just as a man, but as a writer. Paul Theroux, who once counted him a friend, but was then woundingly discarded, believes that Patrick French's authorised biography “will probably destroy his reputation for ever”. John Walsh, writing in The Independent, says: “Perhaps, like Iago, he just enjoys his own treachery. Perhaps having the Nobel prize tastes sweeter when you can tell the global village you don't want their vulgar adulation.” And Yasmin Alibhai-Brown in the Evening Standard declares that she will never buy another book “from this egomaniac”.

Her argument goes farther than just expressing distaste for Naipaul's private life. “Writers don't have to be saints,” she says, “but they do have to have empathy and live as civilised beings within the rules that apply to us all... Artists are part of our world and must be judged as others are. They cannot claim immunity from decency.”

It's a dangerous argument - and, ultimately, a false one. Great writers do not always conform to “the rules that apply to us all”; indeed, breaking those rules may well be the defining quality of their lives. Step forward Sir Thomas Malory, burglar, rapist, sheep stealer and would-be murderer, who spent more time in Newgate Prison than he did in the drawing rooms of London. Ben Jonson was a killer, who also betrayed Naipaul-like tendencies, being described as “a great lover and praiser of himself, a contemner and scorner of others”.

Was Byron a lesser poet because of the allegations of marital violence, incest and sodomy that hung around him? His treatment of Lady Caroline Lamb, reduced to a skeleton by the cruelty she suffered at his hands, was only one of the many scandals that branded him “mad, bad and dangerous to know”. But no one, to my knowledge, has ever relegated his poetry to the second division of English literature because he was judged to have been a sexual predator.

Biographies, as the author Michael Holroyd once wrote, are at “the shallow end of history”; they have little to do with the work itself. As Holroyd added: “The essential truth is simple: Flaubert was born. Flaubert wrote his novel. Flaubert died. It is his work which is unique, that matters, not the ordinary experience he shared with so many others.”

And if the work is strong enough, it will survive the sleaziest of disclosures. Knowing, as we do now, that H.G.Wells was a sometime admirer of Stalin and a strong believer in eugenics has done nothing to chip away at the popularity of The Time Machine or the War of the Worlds. I doubt if Jean Genet, vagabond, pederast and petty thief, would rank high on Alibhai-Brown's Christmas card list, but I imagine that history will judge him more by Jean-Paul Sartre's description as “Saint Genet” than by the list of his previous convictions. As for Elias Canetti, another Nobel prize-winner, whose treatment of Iris Murdoch and several other of his many lovers showed a contempt for women that makes Naipaul pale in comparison, his reputation simply grows.

The same, I have no doubt, will be true of Naipaul, who has so brilliantly chronicled his long and painful journey through the modern world. The reviews of French's book have, not surprisingly, concentrated on its more sensational revelations, protraying Naipaul as egotist and bully. But his own humanity is not in doubt. I met him only once, over lunch, soon after the death of my father. I told him a little about his last days, and then looked up to find Naipaul had tears streaming down his face. My account had reminded him of his own father - the inspiration for The House for Mr Biswas - and his emotional response was immediate and uncontrollable.

Nor is the picture that emerges from French's biography that of a mere monster. Rather it portrays an immensely complex and often self-contradictory character, with astonishing insight into the human condition, who does not hesitate to expose its flaws as well as its virtues. He can be unforgiving, contemptuous, dismissive - but he is never less than passionate. He is journalist as well as novelist, and though the balance between the two may be occasionally uneven, his journey is never less than absorbing.

The critic Karl Miller describes him as “someone with conservative leanings who nonetheless writes movingly about the poor... a compassionate man who is also fastidious and severe”. Another reviewer noted his “characteristic mixture of tough-minded materialist analysis and atavistic horror”. And the poet Linton Kwesi Johnson said simply: “He's a living example of how art transcends the artist 'cos he talks a load of shit but still writes excellent books.”

Far from destroying his literary reputation, I suspect that this biography will enhance it. By refusing to censor its worst secrets, by allowing French free access to all his papers, by guaranteeing his right to free expression and complete independence, Naipaul has demonstrated that in the end the truth is more important than the image. And that is the emblem of a great writer.

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