Move over James Bond, Britain has a new hero - and he's still at school

He has a worldwide fan base which has already bought more than nine million of his books. But as his core audience is 12-year-old boys, the British author, Anthony Horowitz, has failed to become a household name - until now.

The premiere tonight of Stormbreaker, the star-studded adaptation of the first of his six novels about Alex Rider, a reluctant teenage spy, looks set to change all that. Even before it was finished, the film, one of the biggest independent British productions in decades, had been sold to every country in the world.

And, unlike the Harry Potter films or the forthcoming adaptations of Philip Pullman's His Dark Materials, the £21.5m budget project looks set to become the first British franchise in years without major American investment. Isle of Man Film came on board early to back the movie, which stars 14-year-old newcomer Alex Pettyfer, with a cast including Ewan McGregor, Bill Nighy, Sophie Okonedo, Stephen Fry, Alicia Silverstone and Mickey Rourke. The rest of the financing includes an 11 per cent stake by the UK Film Council, which may prove lucrative if the movie is as popular as the books.

Horowitz, who is also a television scriptwriter for series including Foyle's War, adapted the novel himself. The producers have already commissioned him to adapt the second book in the Alex Rider series, Point Blanc.

Horowitz, 50, said he hoped the movie would be the start of a new franchise. "If Stormbreaker is a success, there will be five if not six more films," he said. "I was nervous about making a film of the book because films can spoil books. The books have had their acclaim in their quiet and contained way, but a film with this budget has a lot more riding on it. But I'm very happy with it."

And although there is a 55 per cent to 45 per cent split between boy and girl readers, the film looks set to attract a strong female following, thanks to the good looks of its lead. "He's very much a pin-up," Horowitz said.

Marc Samuelson, co-producer with his brother Peter, said very few films of this budget were put together outside the American studio systems. Samuelson, whose work includes Wilde and Arlington Road, had employed Horowitz as the screenwriter for the 2002 film The Gathering, and had lobbied him for the rights to the Alex Rider books even before the first was published.

Neither wanted the story re-written with Rider as an American hero. They turned down an approach from a US studio to finance it fully for that reason. Instead, the quintessentially British story, which goes on general release on Friday, was filmed on location in London, the Isle of Man and at Pinewood Studios.

Samuelson hopes the result will also entertain adults. "I've got two daughters and I've had to sit through some unbelievable drivel [at the cinema]. But there's an intelligence and wit to this that I hope will appeal to adults too," he said. "All I've ever wanted to do was build a really substantial British film company. If we can do it on the back of this, and make a lot of money, that will be rare and wonderful." Horowitz said: "No one has actually given credit to the Samuelsons for producing a British action movie that takes the Americans on at their own game and does it on our own terms. It makes me very pleased."