"Stella is sexy!" Ruth Jones on the return of her comedy alter ego

"I’ve been offered a couple of theatre jobs and there have been TV offers as well," she says. "I’m complimented to be thought of, but it just wouldn’t work. You know, 'I’ll try and fit in a day’s filming' but it’s never really a day’s filming. It requires a lot more work than just turning up on the day. I just think there’s no point in spreading yourself thin. You’ve got to commit wholeheartedly to what you’re doing and do a good job at that rather than do an average job on lots of things."

She's done a good job so far. Set in a Welsh valley town and centring on Jones herself as a divorcee with a chaotic extended family, series one of Stella kept the warmth, slyly filthy humour and brash but believable characters of G&S, extending its scope from sitcom to comedy drama. Simple and watchable but too funny to tip over into soap, it was a critical and ratings hit – maintaining that is the task that now takes up all Jones's time and effort.

At one point in our conversation she says "There wouldn’t be Stella without Gavin & Stacey and I’ll always be grateful for that", almost as if one of the biggest sitcoms of the past decade was merely a stepping stone to the one she really wanted. She doesn't feel that way about G&S at all, of course, but the statement's a measure of how much of herself Jones has poured into Stella.

So when it came to the second series, was it easier because the characters were all in place, or harder because they needed reinventing? "Because series one ended on such a cliffhanger [the love triangle between Stella, her boyfriend Shaun and her old flame Rob] we knew where we could take the second series. But we wanted to look at other characters’ lives for storylines, so that’s why Paula and Dai [Elizabeth Berrington and Owen Teale] get a very strong storyline in series two, which very much starts in episode 1 and finishes in episode 10. Same with Emma and Sunil [Catrin Stewart and Rory Girvan].

"It’s always good to throw things at characters that they’re not normally used to experiencing. I’m talking about them as though they’re real people..."

The focus, however, is still on Stella herself. Jones runs the show behind the scenes, but her performance as the titular lead character is just as important in terms of setting the programme's tone. It's an unselfish bit of self-casting. I ask Jones: you had carte blanche to create whichever role you wanted for yourself, and you chose someone unglamorous and crumpled who makes a lot of mistakes. You could have played someone sexy and successful.

"She is sexy! She’s not aware of her sexiness, it's a natural thing because of somebody loving her. And she’s this lioness of a mother so it’s her default to put her kids first."

If you could sit down with Stella, what advice would you give her? "I really like her because she is so fallible, and she’s got a good heart. She thinks of other people but she’s not totally downtrodden. My advice would be for her to carry on as she is. Her attitude to life is amazing, she doesn’t take herself too seriously. She’s a good friend and a good person to be around. I love her compassion."

Some writers would spend a long time thinking about what message they were sending out with their female protagonist – particularly a 40-something single mother (and now grandmother) protagonist. They'd want to be making a statement about her, and real people like her. But that's not how you work, is it? "It doesn’t bother me. I don’t feel any responsibility to use Stella to make a point to tell people how to live their lives. For me, she’s a human being with the frailties and the great things that human beings have. She is a very loving person, she’s loyal. She gets a bit paranoid sometimes, she thinks she knows what’s right and she doesn’t."

I think the best thing about Stella, and Gavin & Stacey, is how unashamed they are about featuring nice people who love each other and regularly express it. Is any part of you hankering to change tack and write something where the people are absolute bastards? "I don’t know if I’d be any good at it! I think it would end up sounding a bit comedic. I had to write a script once where some scenes were set in the Houses of Parliament - it was a government initiative about teenage obesity and it was dreadful because I didn’t know what I was talking about."

Shows with no baddies could easily turn to mush. Stella doesn't. But it could. "We have got a couple in this series. But you have to be true to the style and tone of the show. There’s a boxing match in episode 8 and we could have made it really horrible, which might have been right for another show but it wouldn’t be true to Stella. It is what it is. There’s no point in trying to make it Boardwalk Empire."

Ruth Jones and James Corden ended Gavin & Stacey on a high, as Britain's favourite comedy, so its creators' next move was enthusiastically anticipated. That can give writers boundless confidence, or it can make them anxious about not being able to repeat the trick.

Jones was very much in the latter category. I was the first critic to see Stella, at a cast screening in September 2011 – when I told Jones I loved it and explained why, her reaction was one of genuine, quite startling happiness and relief, an emotion established writers don't normally feel. Even then, there was still the public to worry about when it was finally broadcast.

"I was very nervous. Because Gavin & Stacey was so successful, I was terrified. When it went out on TV, David was monitoring it on Zeebox. I don’t do any of that: Zeebox, or Twitter. Not for any grandiose reasons, but because I don’t want to know what people are saying about me, and I don’t want to tell people what I’m doing with my life.

"I said to David, 'Don’t tell me, I don’t want to know.' Then at the end he went: 'People really like it.' Thank God for that! But even though the first series went very well, I don't feel any more confident about the second. I’ve already told David that I don’t want to know about the Zeebox thing. It’s like: the more you go on a plane, the more chance you’ve got of being in a crash..."

Jones had already seen her friend Corden suffer a backlash. He's recovered handsomely now, but his first projects after Gavin & Stacey were heartily panned. "It was difficult for James, because his sketch show [Horne & Corden] came out very soon after Gavin & Stacey. If it had gone out at another time, it wouldn’t have been slagged off as much. There were really funny characters.

"James is working on this new show The Wrong Mans [for BBC2] and I’m sure he’ll be nervous about that coming out. But the pilot is brilliant. And there’s worse problems in life."

Do you ever think that it’s great that people like Stella, but if it was on the BBC instead of Sky there’d be twice as many of them? "You can’t help but wish that more people could see it because it’s something we’re so proud of. You go from 10 million viewers watching Gavin & Stacey to 1.5 million watching on Sky, but on the other hand, it was Sky who encouraged us to make it. We were a new company, they took a risk with us and we’re very grateful for that. And I’m actually amazed by how many people have seen it. A lot of people have bought the DVD. When we were doing series one people would be shouting 'Nessa!' in the street. Now people shout 'Stella!'"

If you wanted 10 million viewers again, you could just do another Gavin & Stacey.

"I watched the Christmas special the other night and it was so lovely. I texted all the cast and said it was such a lovely time, and it’s such a good show, I’m so proud to have been involved in it and I hope we get to do it again one day, even if we’re all in sheltered accommodation by then. Larry Lamb texted back: 'It’s alright for you young ones, I can’t do it from six feet under'!

"We thought for a while that we would do a special and then it didn’t happen. There are no plans to do it. We just don’t have time. James and I literally don’t get to see each other. It’s a shame, but it might change at some point."

Until then, Jones is all about Stella. You don't even see her popping up on panel shows. "The reason I don’t, because I do get asked to do them, is that I’m just useless on them. I did Just a Minute on their anniversary. I thought I’d be alright at that because it’s just improvisation, but Paul Merton’s quite strict and he gave me quite a hard time. There are people who do it all the time on Radio 4 and are brilliant at it - you have to come in all guns blazing, otherwise they’ll knock you down. It’s a skill to go on a panel show: quick-wittedness, which I don’t have. Mine’s more of a slow burner."

You're happy being known just for your work? "As I get older I have to concentrate harder, so I just go, right, this is the job in hand now. I get my head down and get on with it. It is a lovely problem to have, yes. I'm enjoying it now while it’s happening. It’s the time of my life."