David Nicholls is hurrying home from talking to a scientist in Farringdon who’s been helping him research his new book, Us.

“The main character, Douglas, is a scientist,“ the 47-year-old shouts down the phone. “In the past, I’ve always written about people who are writers or actors or students, all things that I’ve been, and I thought I should write about something which I knew nothing about. So this one is a biochemist – and I’m now desperately trying to find out what that means!“

Us – about a couple looking back over 21 years of marriage as they go on one last family holiday around Europe with their son before they “may or may not split up“ – came out last September, and is just one of the things that the writer of the runaway bestseller One Day will be talking about when he comes to Chorleywood for An Evening with David Nicholls, for the Chorleywood Bookshop.

“I haven’t done an event like this for a while because I talked about One Day a lot and I promised that I wouldn’t again until I had something else to talk about as well,“ laughs David, who also wrote the screenplay for the subsequent film that starred Anne Hathaway and Jim Sturgess.

“They’re great because you need to be reminded that people actually buy and read these things you’ve written, that they actually respond to them and are enthusiastic. Also, I get to leave my house, which I don’t do very much!“

There will be plenty of ‘something elses’ for David to talk about: he has also written the novels Starter for Ten and The Understudy, as well as the screenplays for the films Simpatico starring Sharon Stone, Jeff Bridges, Nick Nolte and Albert Finney, And When Did You Last See Your Father? starring Colin Firth and Jim Broadbent, and Great Expectations, with Helena Bonham-Carter and Ralph Fiennes.

His TV credits include episodes of Cold Feet, the cult 1990s series, and Tess of the D’Urbervilles, starring Gemma Arterton and Eddie Redmayne.

As well as the new novel, he also has a film version of Far From the Madding Crowd due out “some time“.

“When I finished One Day, for about three years I found it very hard to write anything at all,“ admits David, who was born in Eastleigh in Hampshire and now lives in Highgate.

“I think I only managed two short stories other than my scripts. I found it almost impossible, I think because I didn’t have a good enough idea.“

The idea for Us came to David when he was publicising One Day throughout Europe.

“I went to a lot of cities that I really should have gone to when I was a teenager, you know, backpacking. I never went inter-railing and it was quite strange seeing them for the first time at the age of 44 instead of 17. And I liked the idea of a middle-aged couple going inter-railing like teenagers.

“I also wanted to write about marriage. My previous books have been about dating, and as a 47-year-old father of two children, it seemed that maybe I needed to broaden my horizons. I wanted to write about family and parenthood and the stresses and strains of a long-term relationship. That makes it sound a bit depressing! It’s still funny and romantic, it’s not a terrible mid-life crisis of a book.“

Has David felt any pressure writing Us, after the enormous success that One Day enjoyed?

“Er, yeah, but I also feel I’ve finally got the balance I’ve been struggling to strike between not wanting to repeat myself and not wanting to do anything so wildly or perversely different that no-one enjoys it.

“There has been a bit of pressure but, as a problem, it’s quite a luxurious one to have and I don’t really want to complain.

“But I do think this book is much better – much more grown-up and a bit more varied in its tone. And it’s still very funny and it’s still very sad, so hopefully people will like it too.“