KNOCKING at the door of Mark Haddon’s semi in east Oxford, I am seized by an irrational anxiety: please God, let there be no dog, because if ever an author were likely to be a cat man, it is Haddon. His novel The Curious Incident of the Dog in the Night-Time begins with the discovery of a murdered poodle: “The dog was dead. There was a garden fork sticking out of the dog,” as Christopher, a 15-year-old suffering from Asperger’s syndrome, tells us on page one.

“That was the genesis of the whole book; just writing that scene and thinking it was very funny,” says Haddon, sitting in his kitchen, a couple of yards from the cat-flap. “Particularly the fork. Particularly the fork going into the ground and staying upright because it’s gone all the way through.” When the image first popped into his head he laughed so loudly that his wife Sos could hear him from downstairs. “Then I realised that you had to describe it in this totally deadpan way to make it funny, and Christopher came along as the owner of the deadpan voice. I thought ‘Yeah, a teenager with Asperger’s would be really good’.”

Christopher, a fan of Sherlock Holmes, decides to become a detective and find out who killed the dog. Unable to read human expressions, or understand all but the most basic emotions, he misses much of what is going on around him. The “murder mystery” is solved halfway through the book, leaving Christopher to unravel the altogether trickier emotional puzzles. One of the great joys of Christopher’s obtuse narration is the sly way it highlights the barmy behaviour of the adults, all presumed to be emotionally literate. There are moments when it seems that it is they, not Christopher, who are the oddballs. He is rational. They are not.

This may explain why the novel was considered as much a teen novel as an adult one. Publishers deemed it a “crossover novel” and brought out two editions, one for adults, one for children. Yet only the covers are different, and the harsh swearing has been kept. “Including the ‘c’ word. That’s a first in children’s literature. Ha ha ha,” chortles Haddon.

The book received thoroughly adult plaudits, including one from Ian McEwan. “Haddon’s portrayal of an emotionally dissociated mind is a superb achievement,” he waxes on the adult cover. Having won a couple of children’s book awards, but been snubbed for the Booker (despite the best efforts of John Carey, the chairman of the judges), it has just scooped this year’s Whitbread Novel Prize.

Haddon claims to be emotionally dissociated from his triumph: “People get excited on my behalf.” A few years back he might have achieved paroxysms of joy, but he has waited so long for acclaim — he published his first book at 22, and is now 41 — that it is as if the moment has passed.

“It’s rather like needing a pee on a long coach journey,” he says cheerfully. “If you get to the service station in time, it’s fantastic and you pee like a stallion. If the service station is slightly too far, the plumbing just jams. It’s like that for me: it’s hard to get excited because I’ve passed the service station.”

He grins boyishly, looking not at all like someone who has passed any milestone. (Though in November his wife, Dr Sos Eltis, an English lecturer at Brasenose College, Oxford, gave birth to their second son.) Having never had “a proper job”, Haddon still looks a little like a student — the hoop in his left ear is pure Young Ones. Still, he has not been languishing in some dingy garrett since he left Oxford in the early 1980s. He has published several children’s novels, worked as an illustrator and cartoonist, and won two Baftas for a children’s BBC drama, Microsoap, which are propped up on the mantelpiece. His adapation of Raymond Briggs’s Fungus the Bogeyman has been produced by the BBC, while his poetry has been short-listed for the prestigious Arvon Prize. On top of all that, he paints, selling his abstract canvases through a shop in central Oxford.

He is not a great believer in research, and did not read any medical literature before constructing Christopher. “I concocted his character from various bits of people I know, often lifted wholesale. He’s obsessed with foods not touching. That’s my niece. He has good days and bad days. I know someone else in my family who has a slightly bizarre numerical method of working out whether it’s a good day or not. I’m obsessed with maths, so that bit came from me. It’s only when you put all those things together that you get someone who would have a label attached to them.”

He has received numerous requests from academics to give talks on Asperger’s, but has always decined. “I never use the word Asperger’s in the book,” he notes. “And I rather wish I could turn the clock back and take it off the cover.” In fact, he adds, “a good friend, a mathematician, said, ‘It’s not a book about a boy with Asperger’s, it’s a book about a young mathematician with behavioural problems’. That ’s the label he put on himself.”

Now the very model of amiable, sensitive manhood, Haddon wasn’t always so joined-up as a child. “Some kids are real naturals in the playground and life is never a real mystery for them. They don’t spend long periods on their own. For another group of people, life is more difficult. Nothing ever falls into their laps. But for them life is also more interesting.” He puts himself in this second category.

“I had an obsession for six months that I was suffering from some dreadful mental disability, but that no one was telling me. The whole thing was constructed to make me think I was living a normal life.” He doesn’t think think this is unusual for boys — another friend had a fantasy in which everyone he met, including his family, was an actor, and his whole life was faked around him, a bit like The Truman Show.

He grew up in Northamptonshire, where his father was an architect. During the building slump of the 1970s he designed abattoirs — “I’m a vegetarian and he took that as a personal affront,” Haddon says. “He also did the Ikea store on the North Circular, which is like an abattoir without the rotating knives.”