THEY said it was a book that could never be adapted for the stage - but the National Theatre’s acclaimed, multi award-winning production of The Dog in the Night-Time has proved that wrong.

“I read the book when it first came out and loved it. I never thought in a million years it would be adapted for the stage - in fact I thought it was a book you couldn’t really adapt,” says Marianne Elliott, who directed the National Theatre’s adaptation of Mark Haddon’s best-selling novel about a boy with autism.

It was reading Simon Stephens’ script, as a favour, that Marianne began to see the potential. “I saw it as a film at first. I thought it was very visceral and incredibly emotional. I had no idea how you’d do it, absolutely none,” she says. “At that time there wasn’t much help in the stage directions for things like Christopher’s journey in London. I just thought it’s an amazing story and he’s found a way to make it work, with lots of voices rather than just Christopher.”

She adds: “In an early draft Simon wrote something like ‘maybe at one point Christopher goes bonkers and dances all over the place - maybe we can involve Frantic’. I knew physical theatre company Frantic Assembly’s work and I’d always wanted to work with them. I knew there were a lot of parts of the play that needed to be staged imaginatively with the actors on stage as opposed to great bits of scenery.”

How did she come up with the idea that the whole stage was Christopher’s mind? “That was a long, long process. For a long time, we were going along the route of it being a play within a play and if it was that, who are the performers? Are they his teachers? Are they his school friends? If they’re his teachers, where are they doing the play?

“Eventually, through lots of meetings and lots of playing with the model box, we thought it should be more magical. I was really keen that it shouldn’t be too high tech; that it wasn’t some great big illusion. Between us we eventually came to a happy place that it should be his brain and it should be a box, and that in the box there are magic tricks. But they’re not down to incredible moving digital scenery - it’s to do with seeing how the humans create the magic.”

Marianne says the role of Christopher is particularly challenging. "It’s a really difficult role and difficult to cast because he has to be young but, inevitably, young usually means inexperienced and the actor has to be on stage the whole time. He has to drive every scene. He has to understand what it is to feel emotions and to feel them very intensely but not be able to identify or articulate them. He’s got to be very adept physically. High demands on all levels and therefore a very difficult part to play. That’s why there are two Christophers - it’s too physically demanding to do eight shows a week because it's such an incredibly demanding role."

The play has won countless awards and has played to over two million people worldwide. What is it that resonates with audiences? "Lots of people relate to having a really inspirational teacher who, amongst the midst of disappointment that every other adult gives you, can see potential in a child. Also, it’s about parenting and about families - parents who are flawed but trying to do their best. It’s also about Christopher - he’s highly vulnerable and highly limited in some ways yet manages to triumph and succeed in a way that’s beyond his dreams."

* The Curious Incident of the Dog in the Night-Time is at the Alhambra from July 31 to August 5. Call (01274) 432000.