ANTHONY Horowitz, the creator of the dazzling boy-spy Alex Rider, has just avoided driving into a bus on an extremely busy road. This skirmish provoked no roof-top car chase or quad-bike battle, it involved no MI6 or exploding bubble-gum, but then that's how Horowitz likes life: humdrum, so he can get on with writing TV dramas, screenplays and bestselling cult children's novels.
Just now, however, peace eludes him. A movie adaptation of the first book in the Rider series, Stormbreaker, is about to hit the big screen and has already been hyped as the must-see action movie of the summer for schoolboys (including overgrown ones) or girls.
Directed by Geoffrey Sax (Tipping the Velvet, The New Statesman), it boasts a golden-haired new teen star in 16-year-old Alex Pettyfer as well as a phalanx of established names - Stephen Fry, Bill Nighy, Robbie Coltrane and Ewan McGregor. Hence the close encounter with the bus: "I suddenly saw, splashed across it, the first ads for Stormbreaker," says Horowitz, words rushing out in all directions like spilt marbles. "It was as if, only then, the excitement of all this hit me. Until a few minutes ago, the whole film business had seemed like standing in front of a huge mountain. I'd created it, I'd written the screenplay and approved the T-shirts. Yet I felt tiny, almost unconnected."
This tall, scrubbed-looking, tanned 51-year-old has a fast-talking, neurotic charm. He worries he's saying the wrong things: too shallow, too deep; dull; repetitive; personal, impersonal; simple, muddled.
At first he tries interviewing his interviewer. It's clear he'd rather it were that way round. While evidently on a high over the imminent film release, he's really happiest when committing words to the page back at home, for anything up to ten hours a day.
After two decades of combining the writing of children's books with TV hits such as Foyle's War, Midsomer Murders and The Gathering, Horowitz struck lucky with the creation, six years ago, of his 14-year-old reluctant spy.
Like Harry Potter or Frodo before him, Alex Rider is a chosen one, an orphan groomed unwittingly for the task ahead of him by his uncle (McGregor), whom Alex thinks is a bank clerk but is, in fact, a top spy.
There, any comparison with other recent literary heroes ends. In fact, when finding himself in a mysterious hidden room in Liverpool Street station, Rider asks with typical teenage disdain: "What is this place? Hogwarts or something?" Is Stormbreaker, then, intended as an antidote to Harry Potter?
"Yes and no," says Horowitz. "There's no magic, or wizards or Quidditch. Instead, there are fantastic gadgets and adventure and modern life with all its dangers. There's London as Londoners see it; fantastic, cool, contemporary."
He delights in the city's role as co-star in this film, and thinks Hollywood should learn a trick or two from Alex's chase, by bicycle, across Albert Bridge. We see Horseguards Parade, Piccadilly, the Science Museum, the Gherkin and Hamleys toyshop, too, as never before.
He continues: "I'm a huge fan of Joanne [JK Rowling]. We're not rivals. Without the enormous wave of interest in children's writing and cinema created by Harry Potter, there'd be no films like Stormbreaker, it's as simple as that."
Whereas Rowling's characters grow older, enabling the same cast to play in each film, Alex Rider is forever 14. Where will that leave actor Alex Pettyfer, who is already two years older than the boy he plays? "It's a tricky one. I haven't seen him for a few months and he may already have turned into a man. He's perfect in the role, though perhaps nearly too good-looking for the part. That worried me at first, since my Alex is supposed to be pretty ordinary, a loner finding himself reluctantly in an adult world and encountering danger when he'd rather play football."
In contrast, Pettyfer is far from average. He was a child model and last year starred in an acclaimed TV adaptation of Tom Brown's Schooldays. He saw off competition from 500 others for this film. His father is the actor Richard Pettyfer, but Alex has been brought up by his mother, Lee, who manages his affairs as well as overseeing the progress of his younger half-brother, a potential world-class tennis player.
"It's an astonishing gene pool," says Horowitz. "To have an amazing actor and a tennis star in the same family. But Alex's head is firmly screwed on and there's no big screaming ego there. I've always said the film would live or die by its central character. We've all seen films flop because of wooden-faced children who can say the lines but don't move their eyes."
Horowitz sees the early teens as a magical time between childhood freedom and the burdens of adulthood. His own two sons, now 15 and 17, have given him news from the frontline and kept him in touch with teenagers' obsessions. Girls, I suggest, don't tend to regard that awkward age as quite so rosy.
"It's hardly a coincidence that I've put relatively few girls in my books, though I now have one in my other series [Raven's Gate]. In a sense, boyhood never changes: it's a time for adventure, danger, adrenaline, even violence. But I'm pretty sure there'll be a lot more girls interested in the books once they see Alex Pettyfer."
He has a point. The (girl) fansites are already throbbing. Horowitz had no such pleasures at that age. He describes himself as rich, fat and cosseted. He grew up in Middlesex, in a large house with servants and a mysteriously successful businessman father, who was later found to have hidden or lost his fortune, the details of which have never been explained.
"I had no adventures, unless you can call hiding in a big north London garden and treating the far end as enemy territory adventurous," says Horowitz.
After his father's death, when Horowitz was in his twenties, the family fortune collapsed, leaving an enigma of coded bank accounts somewhere in Switzerland. "As a result I have an uneasy relationship with money. It didn't make him happy, or my mother. I'm more comfortable with enough, rather than too much."
If Stormbreaker is a hit and Point Blanc, Skeleton Key and the rest of the series are subsequently made into films, he'll be drowning in cash. "When it gets to that stage, I'll give it away." Already a high-profile donor to several children's charities, including one for survivors of Chernobyl, he's a busy philanthropist.
"I love what I do. I'm proud that even if it does little good, it's not doing anyone any harm. It's not sending troops into Iraq."
One surprise about Horowitz is that he was not a great reader as a child, starting with Enid Blyton and graduating, cautiously, to Tintin. "It suited me because there were pictures and not too many words. I suppose I'm writing in that mould of adventure." He also names Biggles ("without the flag-waving"), Bond's creator Ian Fleming and Scottish author John Buchan as inspiration.
"I was never a crusader for that middle-class, stick-beating thing about reading being good for you. You don't get a merit badge for it. No-one is improved by reading The Da Vinci Code, except Dan Brown, who clocks up another sale.
"That view is bound up with class - it's about little Johnny in Kent, who is white and whose parents are bankers. I have nothing against them. They're my readers, I know from the kind of schools which invite me to speak to them. But through the film I want to reach those who regard reading as an alien activity, and show how much of a pleasure sitting down with a good book can be."
Horowitz addicts will detect several changes in the plot of the film version of Stormbreaker, especially the new climactic ending. The violence has been toned down to suit a PG rating but, the author argues, since he has masterminded the alterations himself, the spirit of the book remains intact.
Hollywood was interested but wanted to transform Alex Rider into an older, car driving, sex-crazed young man. Horowitz said no. Nonetheless, boy bloggers seem horrified at the news of some minimal love interest in the form of Sabina Pleasure (Sarah Bolger).
"There's absolutely no smooching, I promise. But yes, there's a quick kiss near the end, which Alex treats with the scorn you'd expect." Alex Pettyfer, on the other hand, announced in a recent interview his desire to travel the world in an old school-bus-cum-love-shack, "picking up a few girls along the way". He seems to have his sights set on Bond next.
"If that's the case I'll take consolation from Billy Elliot, where they found brilliant replacements," Horowitz says philosophically. "There are different Bonds. Why not different Riders?" And then, perennial worrier that he is, he's off again: "If there is another film, if this one is a success..."
• Stormbreaker opens tomorrow. See our review on page 30 of today's paper.