Mark Haddon has already said he had “no idea” that his novel about a dead poodle in Swindon and a boy with behavioural difficulties would become a publishing phenomenon. But that doesn’t stop a woman listening to him speak at London’s Criterion Theatre wanting to know at least when he knew The Curious Incident of the Dog in the Night-Time was going to be big globally.

It was while sharing a London taxi with his agent, and listening to her take a phone call. The Italian rights were being auctioned. He was stunned, unaware that the then unpublished manuscript had even left Britain.

”On the one hand it was hugely exciting, but on the other quite frightening. It was like driving along a motorway in your car and suddenly wings come out and part of you thinks, ‘Wow, this is the fantasy I had when I was eight years old,’ and part of you thinks, ‘Dear God, how do you control this thing?’”

Curious Incident concerns the efforts of Christopher, a 15-year-old boy who has Asperger’s syndrome, to find out why his neighbour’s dog was killed - skewered to the lawn by a garden fork.

For those who have not read any of the 36 translations - “which only leaves Rockall and Mars to go”, Haddon notes wryly - the medical condition at the book’s core is related to autism. Sufferers inhabit a rigorously literal world, one experienced without emotion or guile. This is rich with explored comic potential and is probably why the book has appealed to all ages. The pleasure comes from a genuine puzzle, but also from a touching main character simply unable to lie in a world full of dissembling adults.

John Mullan, senior lecturer in English at University College, London, is interviewing Haddon in front of an audience gathered for the Orange Word lecture series. Mullan wonders about working in a style purged of metaphors (Christopher, as narrator, considers them heinous, because “people do not have skeletons in their cupboards”, literally speaking). Haddon compares it to “a high-fibre diet”, a healthy option forcing him to find clarity without the usual literary props. This crops up again later when a man in the audience wonders why Curious Incident has been so popular. “To some extent the book is very British, but it’s also very simple and clear and not very tied to the English language, actually, because it’s not very metaphorical.” Haddon adds that it’s also “very easy to translate and that gives it a certain universal aspect”.

At 42, the writer is a confident raconteur with a laconic, home-counties style that is neither self-deprecating nor self-aggrandising. Curious Incident was his sixth attempt to escape what he calls “the ghetto” of children’s writing, where he enjoyed success, with 18 novels published.

Haddon, who is married with two very young children, physically resembles former England rugby captain Will Carling and is dressed in thick-soled shoes with brass eyelets, completing the lecturer-chic with an earthy tweed jacket.

He receives lots of letters and “can’t resist” sharing one of the weirder ones. “It was in big psycho-killer capital letters and made no sense whatsoever, apart from the last paragraph, which said: ‘Air Crew. Shot down over the Ruhr. 1942. Pitchforked by locals. Loved your doggy book.’”

Haddon clearly prefers to be seen as jobbing author, not medical condition missionary. The image of a forked dog on a lawn “which, frankly, I thought was hilarious”, came first as he sat at home in Oxford. The key to his enormous success came second: “Then I realised it was much, much funnier if you described it in a very flat, monotonous voice; the voice of somebody who didn’t understand that it could possibly be funny.

”I never sat down to write a book about disability, and I suspect if I had done, it would have been dreary and worthy and very unentertaining.”

The result won the Whitbread Prize last January, a consolation for not even being short-listed for the Booker, which went to Vernon God Little by DBC Pierre.

Curious Incident had, by the Whitbread, sold more than 150,000 copies in hardback alone. Haddon thinks some of its success is because many of us exhibit similar behaviour to Christopher, and empathise.

”I think it’s true that we’re all like Christopher in that everyone in this room is made to feel comfortable and safe by sticking to timetables, rules and patterns.”

As if to prove this, a young woman asks an Aspergerish question about the thin typeface used in Haddon’s book. “I wondered if you could tell me a bit about that?” she says.

It represents Christopher, Haddon says. “It’s typographically plain, in the way that everything he writes about is plain.”

The audience murmurs its appreciation. The author is evidently right: few of us may display behavioural tics to a clinical degree, but we clearly come closer than we might care to admit.