Killer instinct: Is Tom Cruise the right man to play Lee Child's savage anti-hero on screen?

One fine day, when Lee Child was five years old, he wandered into the Elmwood public library in Birmingham and picked up an illustrated book called My Home in America. It was to become his favourite, much-thumbed book.

Among all the pictures of children in their far-flung homes – a New England colonial "saltbox", a prairie farmhouse, a Californian beach house – he always turned to the one of an apple-cheeked boy who lived in New York. It showed him at his window on the nth floor of a skyscraper, gazing out at the Empire State Building. I go to see Lee Child on the 12th floor of a skyscraper in Midtown Manhattan. He is gazing out of the window at the Empire State, only 10 blocks north.

"I was that boy," he says. "Not a boy living in Birmingham, England. It was like I had been trapped in the wrong body." Albert Camus said that, "All fiction rectifies reality in accordance with a metaphysics." Lee Child has rectified it in accordance with My Home in America. For once the phrase "living the dream" is not an exaggeration. At around 6ft 4in and approximately as suave as Cary Grant, Child is now fully grown up, yet he retains something of the innocence and charm of the five-year old he used to be. Just less grubby. And he can use quite long sentences. Although he often doesn't bother. He is the Clint Eastwood of writers. Sardonic. Succinct. Pithy.

He modestly calls this space his "office". But the word conjures up the wrong image. At the very least it would need an adjective such as "palatial", what with that spectacular view, and being roughly the size of the Daily Planet office in Metropolis, where Clark Kent could very well be dashing off another article.

Lee Child recently knocked JK Rowling off her throne. He is the first British writer since her to bestride the top of the bestseller charts in all formats on both sides of the Atlantic. The era of wizards and magic wands and broomsticks is over. Harry Potter is dead, long live... Jack Reacher.

Reacher is a man's man, a charming monster of machismo, all of 6ft 5in and 18 stone, with arms like Popeye's and fists the size of cauliflowers, who casually dispatches a half-dozen heavy hombres without working up a sweat, and flicks any drops of someone else's blood off his sleeve before going off on a date with a beautiful woman. And no Bruce Lee-style kung fu antics either, thank you. It's all fists and elbows to the gut and – his trademark move – the classic head-butt, guaranteed to knock anyone senseless.

But perhaps it would be truer to say that he is a boy's man, just the kind of no-nonsense, ramrod hero an intelligent five-year old would dream up: a strapping, broad-shouldered, idealised father-figure, something akin to God in his wisdom and power, alternately benevolent and overwhelmingly cruel, fair but firm. Good at saving damsels in distress and sorting out bad guys.

Not to mention helping out old ladies. The name of his protagonist first came to Lee when one such lady asked him for his assistance in a supermarket. "Young man," she said to him. "You've got nice long arms. Could you reach that tin of cooked pears for me?" His wife gave him a sarcastic grin. "Oh well, if the writing thing doesn't work out you can always get a job as a reacher in a supermarket." And so a new action hero was born. A military cop turned maverick drifter and vigilante – like an immense, overgrown boy scout.

"Most writers are frustrated musicians," says Lee, as I admire the collection of groovy electric guitars scattered about his office, leaning in odd corners, or draped over the rather roomy bookcase containing all the foreign-language editions of his globally successful series of novels. "Stephen King is the same. He says he'd give it all up to become a rock star." I have a feeling there are a few rock stars who would gladly change places with Lee Child.

"Coffee?" he asks. I take it black, like Reacher, who drinks gallons of it per novel. In fact, I have to, since Child doesn't have any milk in the fridge. Yes, it was just what the five-year old boy would do: no more milk for me, I'm going to drink only black coffee when I grow up. And smoke (Reacher gets through a packet of Camels a day).

Even in Manhattan, he still supports Aston Villa, his childhood team, and worries from afar about their troubles. I suspect he could probably buy Aston Villa now. I don't ask how much he is making from his books. It must be something colossal as the Reacher books have sold 40 million copies around the world.

At this particular moment Child is worried less about Aston Villa's latest results than the first film adaptation of one of his novels, now shooting in Pittsburgh. To clarify: you couldn't really say that Child worries too much about anything. He is probably the most serene writer I have come across. ("When you have a million satisfied readers, you don't worry too much if 100 are bleating.") His brow is rarely furrowed. But he is concerned to explain something that has been widely misunderstood. His most ardent fans have been outraged by the selection of Tom Cruise to play Jack Reacher in One Shot. They say it's a "betrayal" and a "sell-out". On the face of it, they have a point.

In the blue corner, we have Reacher: XXL, so far into the super-heavyweight division you feel the need of another division on top. Undefeated in 1,000 punch-ups. In the red corner, Cruise: lithe, athletic but lightweight, not someone to whom you would readily apply the epithet "rugged". I'm not saying he is short, either, but if Reacher is the Empire State, Cruise is more the Dunkin' Donuts across the street.

When Cruise auditioned for the part, it was not quite (as per the classic Peter Cook and Dudley Moore sketch) a one-legged man applying for the part of Tarzan. But it was close.

Cue outrage.

Child leans back in his white ergonomic swivel chair and runs a hand through his lustrous hair. "To get a film made, you need a name. And the thing you have to bear in mind about Tom Cruise is that he is a great actor, technically he is brilliant." (Another point about Lee Child: I have never known him say a harsh word about anyone – well, maybe Martin Amis, but apart from that.) "If you are looking for someone to play Jack Reacher, do you look for someone with size 15 boots or do you look for the best actor?"

In his previous incarnation as a Granada television producer, Child worked with many greats, including Olivier and Gielgud. "[Cruise] is at the Paul Newman stage. He can't get away with just being young and good-looking any more. He has to mature. He is ready for a transformative performance. This could be the film in which he does that."

Child espouses the classic Existentialist code of self-reinvention. When he got the push from Granada in 1995, he was about 40 years old and decided to recreate himself as a thriller writer, almost like a cartoonist re-drawing his character. And it wasn't the first time he had undergone a metamorphosis. Born Jim Grant in Coventry, he studied law at Sheffield University, where he met his wife, a New Yorker. When they were once on a train rumbling across the US, they fell into conversation with a Texan, who raved about his new car, partly because it was European – a Renault 5, then boldly marketed in the States as "Le Car". But the Texan, rather than pronouncing "Le" with a French accent, stuck to Texan English and called it "Lee Car". After that the word "lee" tended to replace "the" in domestic dialogue between Child and his wife: "Could you pass lee salt, dear?" and so on. When in due course they produced a baby girl, they were bound to refer to her as Lee Child. And when the new author was fishing around for a snappy new pen name to go with it, the nickname came into his head and Lee Child was (re)born.

"You can't become a writer unless you had word games in the family as you were growing up," he says. Pure chance and wordplay. But at the same time I can't help noticing the obvious: the freely chosen identity that has morphed into his real everyday name (Jim Grant is virtually forgotten) spells out "the child"-like element in his work. For example, you will never find Reacher going to the laundry or doing the ironing. When his k clothes get dirty he simply goes to the local hardware store and buys a functional pair of chinos and a workman's shirt and stuffs the old ones in the bin. No mortgage, no wife, no ties, he is a perfectly free agent, unlimited and unbound, incapable of ever settling down.

One Shot, by the way, is a wonderful novel of murder and mystery and resolution, comparable in plotting and craft to an Agatha Christie whodunit, but translated into the American hardboiled, pulp-fiction universe. Child is not in the least concerned about seeing his novel taken to pieces and stuck back together again as a film. "It's a great screenplay – by Chris McQuarrie" (who wrote The Usual Suspects). "And what you need with a good script is someone around to defend it. But since Chris is also directing it, I don't have to worry about that – I know he will protect it."

Protection: it is something at which Jack Reacher is particularly adept. He is an extremely large guardian angel, with only a detachable toothbrush in his pocket. Child, not unlike his own hero, has a cool head in hairy 50:50 situations. Bad guys tend to back away from him. He recalls one time back in Manchester when he was walking down the street late at night and a big scary dude was coming towards him. Child was thinking about crossing the street to avoid him, but didn't want to lose face. And then the other guy crossed the street. To avoid Lee Child. Who clearly looked as if he could be a bit of a bruiser.

The thing about Reacher is that he is not just a thug, even if a well-meaning thug in the manner of, say, Rambo or Bruce Willis. He is also a thinker, an intellectual, capable of quoting Nietzsche or coming up with the etymology of "vagrant". And he speaks French. "He is like a gorilla that can paint," says Child. He therefore brings a certain amount of liberal-leaning finesse and élan to his encounters. He is sympathetic to deserters from the Iraq War and particularly severe on capitalist profiteers. You feel he would probably turn up at an Occupy Wall Street demo. There is something of the hippie in his rootless roaming around America, seeking out injustice and righting wrongs.

How do you start off as a hardcore sleuth, capable of kicking miscreant marines' asses, and end up as a nomadic noble savage? Another of Child's metamorphoses. One of the many virtues of his latest bestseller, The Affair, is that – in this, his 16th novel – Child finally gets around to explaining how Reacher has come to his present state. This is a genesis narrative told in the first person in which his most erotic scenes yet (woven into the passing of a thunderous midnight express) and several extremely unpleasant murders, end up with a resurrection – Major Reacher's rebirth as Jack, unkempt, unshaven and out of uniform, a loner, avenger, perpetual outsider at odds with the army.

I might as well confess. I am a Reacher addict. A Jackaholic. From the moment I first picked up one of his books, I was lost. Worse (as far as objective journalism goes), I have a soft spot for Child himself. He is half-God and half-five-year-old boy, Father and Son. I also, of course, hate the enemies of Jack Reacher. When I read pompous, snobbish critics who deride the minimalist Child vernacular, I consider making comparisons to Flaubert, Proust or Joyce, or point out that the genealogy of the action hero goes back to Homer and beyond. But in truth I would rather track them down and snarl, "You must be confusing me with someone who gives a shit about what you think." Or, "There are two ways you can leave. You can walk out, or you can be carried out in a bucket." Or just give them the good old head-butt.

I started reviewing Child's books because I couldn't wait for them to come out in the shops. Then a friend said to me, "The only way you are going to find out any sooner what is happening to Reacher is by leaning over Lee Child's shoulder and sneaking a peak at his computer screen." Which is how I come to be here at Lee Child HQ in New York. This is my pilgrimage. The good news is that he is already 5,000 words into his next adventure and if only people like me would stop bugging him for a while he could get on with the job.

But he did have time to tell me the secret of being a great writer. "First of all you have to be a great reader." Sitting in front of his screen, he asks himself: what would the reader ideally like to happen next? And he can still lose himself utterly in a book. He recalls one Christmas Day, when he was supposed to be getting ready for a visit from his daughter, being completely absorbed by Val McDermid's A Place of Execution and secretly praying she would be late, unready as he was for any serious responsibilities such as fatherhood or getting dinner on the table.

Just as when he first picked up My Home in America, he can still be that apple-cheeked New York boy, floating in the clouds, on top of the world.

'The Affair' is published by Bantam Press, priced £18.99

Reacher's progress: The anatomy of a crime-fighter

'Killing Floor', 1997

Child's debut thriller – a punchy introduction to the nomadic, ex-military man Jack Reacher. While leisurely following the trail of a deceased jazz musician, the rugged anti-hero is accused of murder, placing him in more trouble than might have been expected from the original itinerary.

'Without Fail', 2002

Reacher is hired to test the strength of the US vice-president's personal protection by performing a dummy assassination. What he isn't told is that a seriously dangerous team are simultaneously attempting that assassination for real.

'One Shot', 2005

Trying to relax, Reacher reclines on a Miami beach with a glamorous friend. Elsewhere, a brutal gun-massacre of five is taking place. When the accused killer asks for Reacher personally, you can assume the order of "Piña coladas for two!" will be grudgingly cancelled. Tom Cruise will star as Reacher in the film adaptation, scheduled for release in 2013.

'The Hard Way', 2006

Reacher's services are wanted by ex-army man Edward Lane in New York – his wife and daughter are being held to ransom. Lane is wealthy and darkly complex – and his first wife did not survive last time this happened.

'The Affair', 2011

Child's most recent novel, released last month. It's 1997, and readers are given a keyhole glimpse into Reacher's past. Still a military cop, this is the case that will result in his split from the army – a young woman has been murdered, and the suspect is a captain.

Compiled by Emily Sargent