THERE’S a buzz in the air when I meet Matt Haig on the outdoor terrace of York’s Grange Hotel.

Everyone is sipping summer cocktails (non-alcoholic) and enjoying the Mediterranean-like sunshine.

The Bootham hotel is hosting a literary lunch, and Matt is the guest of honour.

The best-selling author – and former York resident – is back in town to promote his new novel, How To Stop Time, and things have never looked so good.

“It’s already a Sunday Times best seller,” says Matt, beaming as he clutches the new hardback – his 14th published work.

But there is even better news to come. Hollywood actor and TV star Benedict Cumberbatch has optioned the novel and wants to play the lead character, Tom Hazard, in the movie.

Tom is a gem of a literary creation. Born with a rare condition that makes him age 14 times more slowly than the average human being, he has lived for four centuries but only looks in his early 40s. The novel is set in modern-day London, where Tom is a history teacher, but also in Elizabethan England, affording a face-to-face with Shakespeare, and in 1920s Paris, when there is a crossing of paths with Jazz Age author F Scott Fitzgerald.

Matt is thrilled at the prospect of the Sherlock star taking on the lead role. He tells me he imagined Benedict as Tom while he was working on the novel. “I had him in my mind while I was writing it. I think very few actors would be able to play a man who looks 40 but has 400 years of baggage to him. There is always a mystery to Benedict; you can’t quite solve him, and that is part of his appeal.”

Matt, who has moved to Brighton with his young family after living for seven happy years in York, says it was such a boost to his confidence when the book was optioned. “It was two weeks after I’d written the second draft that I learned that Benedict Cumberbatch was to buy the film rights and wanted to be Tom Hazard. When I was writing the third and fourth draft, I was thinking of him, and it helped the book. It can get very neurotic when editing a book, so that early endorsement was great.”

Matt suffered from depression for many years and several of his books reflect this, including his last work, Reasons To Stay Alive – an open letter to his younger, anxiety-ridden and suicidal self.

In the new novel, Matt says he wanted to write about time, because the actual concept is “very therapeutic”. “When I was ill with depression in my 20s, time was something I thought about a lot. Time is one of the things that is bigger than depression. When I was depressed, I’d say ‘you’ll be dead by Christmas’ or ‘you are going to lose everybody’ but time disproves that. It makes you more optimistic.”

He says he’s always been drawn to outsiders. “The idea of writing about an old man appealed to me. When I came out of my mental illness I felt like a 430-year-old man.

“I am a hypochondriac and am always worried that I am suffering from some fatal illness. So I tried to imagine the other situation: ageing slowly – but if you were the only person it would be slightly terrifying.”

Ultimately, the novel has a big philosophical question at its heart. “If you had 15 times more future than we have – how would you live?” asks Matt.

How To Stop Time was the most enjoyable book he has written yet. The history graduate had to return to his academic roots to research the various periods of Tom’s life and give his back story realistic shape. This was new for Matt who normally writes in the present day or simply uses his imagination (previous books include The Radleys, about a York family of vampires and The Humans, about an alien who comes to Earth).

“This is my first, proper, historical book. And it took a lot of research: it is like 12 historical novels in one. It was fun, but a bit daunting. For the dialogue, I just went with what sounded right.

“I read a lot of social history because I wanted to be accurate enough and conjure the feel of the place.”

Matt may write about outsiders and seemingly unbelievable worlds. And yet, his characters are a means to explore the very essence of the human condition. It’s heavy stuff, for sure, but written in a light and readable way.

He says: “Fiction is a better way of getting at reality. Sometimes it is easier to get at the truth on a deeper level by going around it.”

How To Stop Time, by Matt Haig, is published by Canongate, priced £12.99