DESPITE her success as an actress and scriptwriter, Ruth Jones is decidedly unstarry, softly spoken and looks much younger than her 51 years. Best known as Stella in the eponymous comedy series and as Nessa Jenkins in the hit comedy Gavin & Stacey, which she wrote with co-star James Corden, Jones is warm and funny, chatting happily about her life in Cardiff with her producer husband David Peet.

Her debut novel, Never Greener, features a young woman who has an intense affair with a married man, which ends in heartbreak. Fast forward 17 years and their lives have moved on. She is now a successful actress, married with one child; he is a teacher still married to the same woman, with three children. Chaos ensues when the actress bumps into him again and the spark re-ignites.

The book first emerged from a screenplay she wrote in 2002 - which never made it to the screen - when people were getting in touch with friends from the past through the website Friends Reunited. "You heard all sorts of stories about people leaving their long-term marriages to set up with people that they were going out with when they were 17. And a lot of those second attempts went wrong."

But it wasn't based on her own life, she insists, laughing. "I married the man that I love. It was love at first voice because I spoke to him on the phone before I met him."

Growing up in Porthcawl, Jones kept a diary as a 13-year-old and another in her 20s which, she says, shows how your personality changes as you get older. "When I re-read my diaries, it's the self-doubt that seems to be prevalent," she reveals. "Since I turned 40, I've become less self-doubting, but it still happens."

Because of this, she isn't on social media. "I couldn't handle it if somebody said something nasty," she confides. "But I have read comments that people have received. James Corden, for instance, gets horrible comments from people. The world is crap enough without adding to that vitriol. People say it's like the modern day graffiti on toilet walls in the pub, or when you're in a car and have road rage."

Her novel attracted a bidding war, handled through her old Warwick University pal, top literary agent Jonny Geller.

"I am nervous about how my debut novel will be received, because there's always that feeling that somebody might say something negative. I say I won't read the reviews, but I probably will."

Apart from a book tour, life will go on as usual in Cardiff with Peet, who she met while working on a comedy pilot in the early 1990s. She has three grown-up stepchildren from his first marriage.

While she has never had children of her own, being a stepmother seemed to come quite naturally.

"You take things as they come. There wasn't a moment when I thought, 'I've become a stepmum now'. We were really lucky. We never had any difficulty with teenage angst, and now I'm looking forward to becoming a step-grandmother at some point."

The couple set up a production company and co-created Stella - doing 58 episodes together - but she says there won't be any more. "It took over our lives. We'd storyline the next series in August when we were still filming the previous series, so there was never a break. We loved it and created some fantastic characters that we still laugh about, but we knew we'd have to move on."

She also says she wouldn't reprise Gavin & Stacey, although she has extremely fond memories of it and remains friends with Corden.

"We used to talk about maybe doing a special, but if you look at the logistics of it, James lives in America and he's so busy. Even if we did write something, when would we film it? James and I still have little conversations about what Nessa's doing or what's happened to Neil the Baby, who is now about ten! We come up with little things that the characters are doing."

She's under contract to write a second book and has several other projects on the go, but these days, she shies away from red carpet bashes and other celebrity events. And she's keen to keep a balance between her professional and her private life.

"If I'm doing a charity event and I'm there because that will give the event interest, then fair enough. People should be able to have their selfies and autographs.

"But the other day, I was in the car and my husband was getting in when this guy came out, looked at me and literally pushed my husband away. He said, 'Are you that woman from Gavin & Stacey?' and my husband was left standing there. I went, 'No, not me'. Sometimes people don't realise they're being rude."

  • Never Greener by Ruth Jones (Bantam, £12.99)