‘I was incredibly naive back then,’ David Nicholls admits as he recalls his first brush with the big time. ‘One evening I was sat at home watching Top of the Pops. The phone rang, and this voice said, “Hi, it’s Jeff here.” I thought it was my girlfriend’s dad, Jeffrey. So I started this informal, chummy conversation.’

The call continued in this vein for several minutes before Nicholls realised that the man at the other end was not his prospective father-in-law. ‘It was Jeff Bridges, calling with his script notes.’ An understandable error. After all, which of us hasn’t mistaken a major star for our partner’s dad?

But this was an important time for Nicholls. It was 1999, and the man who would go on to be the literary sensation of 2009 with his novel One Day had been given the chance to collaborate with playwright-actor Sam Shepard on Hollywood thriller Simpatico, which counted Bridges and Sharon Stone among its cast. ‘Yeah, I lucked out on that one,’ says the 45-year-old with modesty. ‘I was still working as an actor at the time, but dabbling in script-editing.’ And how did he overcome the embarrassment of not recognising one of the film’s stars? ‘I just had to try not to laugh.’

But what an appropriate starting point for the one-time bit-part actor from the UK county of Hampshire, who has gone on to master the dynamics of the modern rom-com as an author and screenwriter. The title of his third novel, One Day, refers to July 15, St Swithin’s Day, the date on which his two protagonists first meet. That day every year is our window to all the later action. As with his previous novel, Starter for Ten, about a lovelorn student attempting to get on University Challenge, this one has been adapted for the screen. Anne Hathaway steps into the scuffed Doc Marten boots of the virtuous, highly principled Emma Morley, while Jim Sturgess stars as her louche and dangerously impulsive foil, Dexter Mayhew. Danish director Lone Scherfig, who captured Lynne Barber’s formative romantic clinches so convincingly in 2009’s An Education, diligently ushers the adaptation to the screen. But when Nicholls finished writing One Day, a frantic bidding war for film rights was notable by its absence.

‘Books and movies are my two great loves, but when you’re writing a book, you shouldn’t be thinking about the film. Though once you’re finished, you inevitably start pondering if it will have another life, and I thought there were lots of practical reasons why One Day wouldn’t work as a movie. For a start, 20 years is a long time. It’s hard to have actors ageing up and ageing down. It goes all over the world, and that’s expensive. I also think the story is driven by a literary device rather than a cinematic one.’

Those stumbling blocks were overcome with ease, and Scherfig’s film, adapted by Nicholls himself, sticks closely to the tricksy timeline of the book. The story begins in 1988 as Em and Dex celebrate their graduation and, as we watch them get older, we also see fashion and culture evolving in the background. While Emma works in a Tex-Mex cantina, Dex becomes a drug-hoovering celeb in the world of youth TV. Both book and film do not present the early ’90s Soho media set, or, indeed Dexter’s hedonistic lifestyle, in a flattering light.

‘I sometimes worry that it’s a judgemental or moral book,’ admits Nicholls. ‘That [it says] if you stay up late and party too hard, you will be punished. And I wouldn’t want it to be preachy, because we all have our moments of not behaving well. But there was a sense in the late ’90s that there was a kind of edge to everything, a spikiness, a selfishness. Hopefully it’s more observation than preaching’.

His next writing gig is under way, a feature version of Great Expectations directed by Mike Newell with Ralph Fiennes as Magwitch and Helena Bonham Carter as Miss Havisham. We ask Nicholls if we’ll ever see his dark side. ‘I sometimes wonder if that would be the thing to do. To write a brutal war novel, on the Russian Front in 1943, and just deliver it to the publisher and see what they say.’
One Day is in UAE cinemas now.