As styled by central casting, Christopher Hitchens is wearing a cream linen foreign correspondent suit and Rayban Aviators. Small and a bit pudgy, he has his shirt unbuttoned to reveal his grizzled chest-rug, known by admirers as The Pelt of the Hitch. He greets me with highly wrought courtesy and the kind of long, blatant up-and-down appraisal that younger men of his class are now too egalitarian to try at business meetings.

Perhaps no journalist is so admired by his peers, in part because he has actually pulled off the life we imagined our profession would afford. Dashing off 1,000 épater le bourgeois words before a two-bottle lunch, blagging through war-zone checkpoints, starry parties, whisky-fuelled late-night geo-politics and crackling media feuds. Yet as most of hackdom has knuckled down to colourless, desk-bound sobriety, there is Hitchens, still larging it, a 3-D cartoon of what we might all have been, given his ego and intellect, his brass neck and neoprene liver.

He is Hunter S. Thompson cut with Gore Vidal, has broken America – as Vanity Fair columnist and a pop-up TV pundit – without even chipping his minor public school vowels. Some believe he is the one contemporary journalist who will still be read in 50 years’ time, the worthiest claimant to the title heir to Orwell.

And everyone has a story about Hitchens, although at 58 he is fed up with the long-lunch legends that undermine his gravitas and obscure serious consideration of his writing. One speaks of him clearing out a minibar in some African hellhole – he still tries to visit “a f***ed up country at least once a year” – and one senior, male heterosexual newspaper executive tells me, not without affection: “Christopher tried to French-kiss me, tried to ram his tongue between my teeth.”

Others recall his generous patronage when they were young journalists, of the soirées at his Washington apartment, which these days are the DC parties to attend. But there is disdain also, and a sense of betrayal. “A busted flush” is how one former admirer describes him, referring to Hitchens’s political gymnastics since 9/11 that have led the former Trotskyite to support the invasion of Iraq and, in 2004, the reelection of George Bush.

Defending the war has cost him prominent old friendships and forged him unlikely new ones, foremost with the arch neocon Paul Wolfowitz. But now Hitchens is back in his most acclaimed role, the dashing prosecutor. And the former tormenter of (among many) Mother Teresa, Princess Diana, Kissinger and Clinton is levelling up to the big guy Himself.

God is Not Great: Why Religion Poisons Everything, although sweeping in its erudition, is a righteous harangue. When Ruth Gledhill of The Times recently interviewed Richard Dawkins about his scientific debunking of faith, The God Delusion, she found him less angry than his confrontational writing style suggested. But Hitchens is never far below boiling point. He is an evangelical secularist, an atheist warlord. Religion, he writes, is “violent, irrational, intolerant, allied to racism and tribalism and bigotry, invested in ignorance and hostile to free inquiry, contemptuous of women and coercive toward children”.

This is the book he has been writing all his life, since his primary school teacher remarked how kind the Almighty was to make trees and grass green, a colour so restful to the human eye, and he knew she was wrong, that our eyes were adjusted to nature, not the other way about.

“Marx says criticism of religion is the beginning of all criticism,” Hitchens says. “Philosophy starts where religion ends, just as chemistry starts where alchemy breaks off or astronomy starts where astrology runs out. It is the necessary argument. Not believing in the supernatural is the critical thing.”

And yet, I suggest, doesn’t it fulfil one function, an innate human desire for ritual? We are soothed by lighting candles or familiar hymns. Secularism, for all its logic, offers no substitute. Surprisingly, Hitchens agrees. He observes Passover (he discovered late in life that he was Jewish, his mother’s family having changed their name from Levin), which his Jewish wife thinks is contemptible. “She never felt she should identify with anything except to be an American. To say you’re Jewish or anything else is sectarian. I should praise that, but why don’t I? Because somehow it would be banal. And I want my daughter to know what the tradition is.

“But I don’t do Christmas because I can’t stand it.” What, no presents? “Well, you have to . . .” A tree? “Er, yup. We went to Kmart and bought a white tinsel one. Actually it’s rather beautiful. Our annual ritual is screwing it together.”

He was married to his first wife in a Greek Orthodox church, to his second, Carol Blue, by a rabbi. He had his son, Alexander, now 23, baptised. He educates his daughter, Antonia, 13, at a Quaker school, Sidwell Friends, alma mater of Chelsea Clin ton and Al Gore’s son. He has taken her to Washington’s Anglican cathedral to familiarise her with the liturgy. He worries that without the scriptures – which he can quote chapter and verse – she will never understand Milton or Shakespeare.

“The point is,” he says, “religion should be private: I am not paying my taxes to support it. I’m not going to have children taught that metaphysical things are true.” America, where secular education has come under protracted attack from Creationists, is “the territory of contestation at the moment”.

“People [in the US] are fed up with the presumption of the religious and the demands they expect to have met. There are many, many more nonbelievers and sceptics in the States and they’ve just about had enough.”

After we meet, Hitchens e-mails me from a book tour of Dixie where, debating a cleric at every stop, he speaks to large and friendly crowds. “Very often,” he reports, “what you find is that almost everyone there believes themselves to be the only other atheist.” His book went straight into the New York Times top ten, “not because of my blue eyes but because it is part of a freshet of volumes [Dawkins and Sam Harris’s The End of Faith] that encourage a fightback against religious bullying and stupidity”.

It is the US constitution’s First Amendment – which enshrines separation of church and state, and freedom of speech – that is the core of Hitchens’s personal credo. He wrote a paean to Thomas Jefferson (with whom he shares a birthday) and last month – after 27 years as a resident – became a US citizen, taking his oath at the Jefferson Memorial. Even his choice of witnesses was confrontational: Ayaan Hirsi Ali, the feminist author, persecuted for her apostasy and criticism of Islam, and a secular Marine just back from Anbar province in Iraq.

While Hitchens’s opponents contend that he has veered right in his defence of Iraq, he maintains that he has simply stayed true to his primary cause: defending secularism and reason latterly against its new, fiercest adversaries, “Islamo-fascists”. He prefers to be known as a Blairite, not a Bushite, he says: “Not to duck the issue. We were right to intervene in Bosnia and Kosovo, and we should have done in Rwanda. I would have supported any president who got rid of Saddam.”

Hitchens has decided that 9/11 is the defining moment – just as the Second World War was to his naval officer father – and fundamentalist Islam is his glittering nemesis. “It is a war to the uttermost with the original form of totalitarianism, which is theocracy. I’ve made a very good living out of freedom of expression and I haven’t had to sacrifice for it yet. And I think it is payback time. And it should come to everyone once or twice in their life. The hour has struck. I regard these people as deadly enemies and I want them to know that I hate them much more than they hate me.”

Would he die for secularism? He has only, as yet, received the odd sinister phonecall. “I’m not going to say that. It’s bravado. But I think it might come to be the case that anyone who believes in unfettered science, sexual emancipation, open society, would have to say they were ready to risk their lives.”

Yet he concedes that Iraq, which he has visited several times, does break his heart: “The difference between our hopes and what has actually happened,” he says sadly. “And I’ve lost friends there.”

As we talk Hitchens smokes his Rothmans and eyes, but does not touch, a bottle of white wine chilling in its bucket. Perhaps his thirst has been quenched by lunch or he’d rather not have me write about his drinking. In our more abstemious age, his legendary alcohol consumption is used to his discredit. Two years ago in a vicious debate on the Iraq War, George Galloway retorted: “You’re a drink-soaked former Trotskyist popinjay . . . Your hands are shaking . . . You need another drink.” And I observe that Hitchens has a curious habit of holding his right hand firmly and correctively with his left.

His wife has remarked that he is a highly functioning alcoholic. He says: “I have never been late for an appointment, never had to cancel a speaking arrangement. I do radio and TV and I don’t slur. I’ve never missed a deadline: you can check that. So it can’t be the case I’m a fall-about drunk. If I needed to prove it to you, I could knock down a lot of booze while we were talking and you wouldn’t notice it.” He drinks, most of all, because it makes other people less dull: “boredom is the terror”.

Anyway, there is no flaw or tremor in Hitchens’s thinking. I’ve seldom met anyone who speaks in such fluid, elegant, nuanced sentences, dizzying in their breadth of reference. His friend, the novelist Ian McEwan, once said of Hitchens: “It all seems instantly neurologically available: everything he’s ever read, everyone he’s ever met, every story he’s ever heard.”

The stories about Hitchens mostly feature his stomach for whisky and dialectic. But I hear enough about him making lecherous grabs at male friends to ask him later, by e-mail, if he is bisexual. He says no. But when younger and prettier, he received much attention from men and at public school he “of course” had homosexual experiences – “everyone did”. He says the rumours probably refer to the time he “smooched” the brother of a girlfriend “who he then very much resembled and it seemed somehow irresistible”. Although, this wasn't the source of the French kiss story.

These days, he says, he’s so decrepit that only women find him attractive. He emits an old-school sexism, a mix of lechery, ostentatious chivalry – he is a hand-kisser – and disregard. He says he has learnt much about women from his middle child Sophia, 18, and envies the easy way that young people enter sexual maturity without the fumbling and embarrassment that he recalls. But he is least insightful when writing about sexual politics, most recently in essays about oral sex and how women can never be funny.

His first wife has forgiven him for leaving her while pregnant for Carol Blue: “I’m invited to stay now. And we’re friends and quite good parents. At the time she was very cross but she says now: ‘When I met you, I realised I was looking for trouble.’

“I have been forgiven and indulged a good deal by women, and God knows what would have happened if I hadn’t been. I’ve been lucky. Though I wish I’d had a sister, though I might have been too well adjusted if that happened. Instead I had a very dramatic baby brother.”

He refers to the Mail on Sunday columnist Peter Hitchens, Christopher’s political mirror image, with whom he feuded for years. Now although hostility has ceased, they seldom meet. I ask if they rowed as children and he says that no, his household was quiet and repressed. Besides he left for boarding school at 8. “He and I are slightly too close in age,” he says. “It made us competitive. The thing I like about him is he really loves railways and loathes motorways. He is nostalgic for a lost and very English idyll.”

But what he can’t abide is Peter’s Christian faith and belief in intelligent design. Christopher has prayed only once in his life – for an erection (unanswered). I wonder whether he envies the faithful as he gets older and death looms, since all that secularism offers in place of everlasting life is “life’s a bitch and then you die”. “Well, that is not said as a gloomy thing, is it? People say it to cheer themselves up.” But it is a dark statement. “There is comfort in noir,” says Hitchens. “There is absolutely no comfort in ‘Jesus wants me for a sunbeam’.”

In his own words... ‘

On terrorism Terrorism is the tactic of demanding the impossible, and demanding it at gunpoint

On drinking How do I do all this and still drink enough every day to kill or stun the average mule? Many great writers did some of their finest work when blotto, smashed, polluted, shitfaced, squiffy, whiffled and three sheets to the wind.’

On free speech There is a utilitarian case for free expression. It recognises that the freedom to speak must also be insisted on for the person who thinks differently. For your own sake, you need to know how other people think

*God Is Not Great, by Christopher Hitchens, is published by Atlantic Books on June 10 at £16.99. Available from BooksFirst at £15.29, free p&p. Call 0870 1608080. timesonline.co.uk/booksfirstbuy