IT'S SOMEHOW NOT surprising that Frank Cottrell Boyce arrives from Liverpool very late, on his way to a meeting with DreamWorks executives who have flown over to see him (not the other way around) about his adaptation of Terry Pratchet's Truckers, and within ten minutes seems like the most fascinating of old friends. He has that slightly chaotic quality about the best children's writers of finding the child in the adult and the adult in the child; and Cosmic - about a too-tall 12-year-old who passes himself off as his own father to go into space on a secret Chinese rocket.

Perhaps best known still as a writer of film scripts, particularly for Anand Tucker (Jackie & Hilary) and Michael Winterbottom (Welcome to Sarajevo, 24 Hour Party People, A Cock & Bull Story), Cottrell Boyce burst on to the scene as a children's author with Millions, an enchantingly funny novel about two young brothers who discover a suitcase full of banknotes which are about to be pulped when Britain adopts the euro. Millions won the Carnegie Award, and, having started off as a film script for Danny Boyle that couldn't get made, then also became a successful film. Beneath the comedy and adventure, it asked profound questions about poverty, goodness and bereavement.

“It was Danny who got me started writing children's books,” he says. “It took six years for Millions to get filmed, and he said: ‘Look, you're always talking about children's books, why don't you turn the script into a novel?'”

Though many children's novels increasingly read like film scripts, he has realised that in scripts “you only write half the character because casting does the rest”. Although there are features in Cosmic that will be familiar to admirers of Anthony Horowitz, Josh Doder and E. Nesbit, he has a uniquely appealing voice, which now in this third book is deepening in its assurance.

The son of a teacher in Liverpool, Cottrell Boyce read English at Oxford, but his experiences of writing scripts for Coronation Street (where he always sneaked in a copy of Marxism Today) are as much a part of his education as his swottiness. Cosmic's hero Liam is an only child, “officially gifted and talented”, whose only friends are online players of World of Warcraft.

Persuading a small girl, Florida, to accompany him as his “daughter” and fooling his parents that he's off on a school trip is, well, child's play. But something goes wrong, and when Cosmic opens, Liam and the other three kids are lost in space; what follows is utterly gripping and hugely funny.

“What's peer pressure about but the pressure to win the approval of people who don't care about you?” says his creator, and it's his vivid recreation of the powerlessness of childhood, the censure and censorship of adults and the joyous independence from it that makes him so engaging as a writer. He writes about adventures that come about through a perfectly plausible quirk of circumstance - such as being an abnormally tall 12-year-old.

“I got the idea from one of my children's friends, who is big enough to pass as a man, and is constantly getting told off, like Liam, as a big boy who should know better. Also, when I was that age I was in an athletics competition with Daley Thompson, and he was already the size he is now. It's not really enviable.”

Alongside J.K. Rowling, Cottrell Boyce is the modern children's author who has most in common with E. Nesbit, but where Rowling developed the magical strands in Nesbit's writing, he has taken novels such as The Treasure Seekers and The Railway Children and retooled their comedy and anguish for modern families. He is well qualified to describe this because he and his wife Denny have seven children.

“We started young, at 22,” he says, drily. Of Irish Catholic descent on both sides, the family spans a son of 22 and a daughter of 4; the last three are being home-schooled. Perhaps because of this, Cosmic is a particularly convincing portrait of the relationship between fathers and sons.

“Liam is an only child, being forced to grow up too quickly,” Cottrell Boyce acknowledges. It's a pressure every child and parent now feels, and which Cosmic explores because, while Liam has to learn to pretend to be an adult, he is in many ways more adult than the real fathers, with their idiotic competitiveness, boring talk about sport and lack of true leadership in a crisis. Liam's anxiety not to upset his father (“Dad, hi, we got a bit lost”, he says, while in dire danger) is excruciatingly funny.

There is no doubt that Cosmic is the best novel he's written yet, not only in combining a pitch-perfect narrative voice and a gut-twisting plot, but in its emotional subtext. It will make a great film, but literary details such as the deadpan parody of a self-help book on parenting teenagers (Talk to Your Teen) which Liam discovers his father has been reading are untranslatable. Needless to say, the appalling child prodigies work together to get back to Earth - but it is Liam who really saves them.

We talk for far too short a time about the complexities of fiction, rocket science and children's need for unconditional love. He quotes the last lines of the parable of the Prodigal Son to me, as the most heartbreaking in literature.

“The best novel about fathers ever is To Kill a Mockingbird,” Cottrell Boyce says. “You think your father is some bumbling old man, and you discover he's Atticus, he's the hero-dad. Liam knows his dad will bail him out. You never feel like you're doing a great job, you think you've got to be flawless, but the most you can do is to be generous and loving and just there.”

Cosmic by Frank Cottrell Boyce
Macmillan, £9.99; 256pp Buy the book here

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