Ashley Jensen opens up about her new role as DI Ruth Calder in BBC's Shetland

Later, when I ask Sharon Horgan, who cast her in Catastrophe, what Jensen brings to a character, she says Jensen has a gift for "making characters feel true" and "aside from being the loveliest, warmest person, Ashley has wattage".

That warm wattage glows in the parts for which Jensen is best known. As Maggie in Extras, she was the sweet counterpoint to Ricky Gervais's cynical, curmudgeonly Andy. As Ugly Betty's Christina, she was a bright and breezy bestie to the eponymous Betty. As the detective lead in Agatha Raisin, she is waspish but never cold; she has the heart of an optimist.

It's in her voice, too, whether she's lending it to animated characters (a flirtatious frog in Gnomeo and Juliet or a dogged dog in Disney's 2019's live action/CGI remake of Lady and the Tramp), telling tales of eye-watering ailments on Channel 4's Embarrassing Bodies, or even selling settees in adverts for an apparently never-ending sofa sale.

To sound reassuring when discussing the world's worst verrucas, or half-price three-piece suites, as Jensen does, is quite the feat.

Jensen's sunniness is a consequence of how she lives her life. She guards her privacy carefully and surrounds herself with good people: "I like people who communicate, who are open, who are honest."

And while she says she feels classless ("I'm not intimidated - I could be plonked anywhere and get on with anyone"), she describes a foundational "working-class sensibility – work hard, have a bit of humility and never take anything for granted". She attributes this to "starting at the bottom and serving an apprenticeship in theatre for years and years".

I first met Jensen 25 years ago, when she was a jobbing theatre actor in Scotland, and she was bright-eyes-and-blue-skies then.

"I think you have to try and be in the here and now, be as present as possible. You have to crack on with it. So that's what I do. And all you can do is be the best you can be, in the moment, as a flawed human being. You get to a certain age in life when you accept that you're not perfect – and you have to stop beating yourself up for it," she explains.

"And my face looks better when I smile. But I think everyone's does." Sunshine is just who she is, even in tragedy; her partner of 18 years, husband for 10 and father to her 14-year-old son, actor Terence Beesley, took his own life in 2017.

This warmth and positivity is at odds with Jensen’s latest role, however, as the new lead in BBC One's Shetland. Following the departure of Douglas Henshall's DI Jimmy Perez, Jensen plays DI Ruth Calder, a Met police officer and a native Shetlander, absent from the islands for 20 years, who is forced to return in pursuit of a witness who is also being chased by two hitmen.

A prodigal return, this is not. Indeed, Calder's reluctance to be home is matched only by her colleague DI Alison 'Tosh' McIntosh's (Alison O'Donnell) bemusement at her discomfort.

In the first episode of the new season, Jensen doesn't smile once. Calder is what Scots would call "crabbit". "The wee morose look of Ruth Calder!" Jensen cackles with delight, teasing that Calder will smile eventually. Probably. Just not yet.

"Because she's from Shetland and she left – for reasons that will become clear as the series goes on – she has history with the place and existing characters, which make her feel familiar. It's a really clever way to introduce a new character."

Jensen said yes to the part on reading one script. "It was so beautifully written, and Ruth so well rounded and interesting, it was a no-brainer. Plus, I really wanted to go to Shetland."

And there's the kudos, of course. "When I started out, there was only the BBC, ITV and Channel 4. The BBC was the one that set the standard, and still does in a lot of ways. Something like Shetland is the standard. It's so classy, and for me to be asked to be part of a flagship BBC show was… wow!"

Wasn't it also daunting? "It's a show that's got such a big fanbase, and going into something as loved as Shetland could be overwhelming," Jensen admits. "I could have been intimidated. But for my own sanity, I had to think of it as a six-part series and focus on playing my story."

Some of that fanbase have grumbled about Jensen joining Shetland and usurping the "rightful" heir to the Henshall/Perez crown – Tosh. But Jensen is having none of it.

"I love working with Alison and bringing in my character shines a light on Tosh, so we see a different side to her. Of course, there will be people who miss Dougie [Henshall] because he was great, but with new directors and a new lead writer, Shetland has kept everything that’s wonderful about it but it’s somehow amplified."

Expressing some bemusement at the thought of women who work together being catty with each other, Jensen says, "It's lovely that it's two women leading the show."

She adds: "As an actor, all you’ve got is yourself. The way I work is to take an element of myself and expand upon it." So what element of herself has she expanded upon to play Calder – whom she describes as "sometimes snippy, frustrated, defensive and not that nice"?

"I came from a small town, Annan [in Dumfries and Galloway, south-west Scotland], which is reminiscent of Ruth. She definitely wanted to escape from Shetland – and escape from who she was when she was there. It wasn't quite like that for me, but I always knew that.

"I was a creative person and it was difficult to be creative in a small town in Scotland. I wanted to get out and explore different places, be it Edinburgh or Glasgow, London or LA."

Jensen's journey took her farther than she ever imagined. "I never thought I'd be on the telly. For me, being an actress meant being on stage, doing plays. My idea of success was, and is, being able to support myself as an actress."

Mission accomplished. But did that make the journey back to Scotland more complicated? Is she one of the many ex-pat Scots who is intensely proud of their homeland as long as they don’t have to go there?

"Returning to Scotland felt like going home," she says firmly. "Work hadn't taken me there for a long time until Mayflies, then along came Shetland.

"For a while, I was conflicted about it, about where I was from. But, I think I needed to see more before I could really appreciate Scotland. Then, when I was back, I ran around buying plain loaves, Scotch pies and Tunnock's teacakes. Now I feel as if I'm settled back with it. I was very happy to be there, with a renewed appreciation for the square sausage."

Before our time is up, we talk about Mayflies, Andrea Gibb's BBC One adaptation in 2022 of Andrew O'Hagan's novel about life, love and loss. Days after we meet, Jensen will be nominated for a Scottish BAFTA for her role as Anna.

"I found it very difficult to read," she says, "because it was all there in Andrea Gibb's sublime writing. You just had to say the words and the feelings came. It was poetic, incredibly sad but weirdly uplifting. I can well up talking about it."

And suddenly we're both welling up talking about it. Then there's a moment when neither of us says anything. It's an eloquent silence that articulates how Mark Bonnar describes Jensen.

They first worked together at the National Theatre in 1998, and then played estranged husband and wife in the comedy series Catastrophe, from 2015 to 2019. "Ashley can be heartbreaking and hilarious in the same moment, showing strength and vulnerability simultaneously," he says. "Simply, she is a truth-teller."

Jensen herself is more diffident. "I know my limitations and that's OK. Maybe five per cent of actors can choose to do whatever they want, but most of us don’t have that luxury. All I've got is this face and this voice, and I'm doing OK.

"Shetland is the first 'drama' I've led [as opposed to the comedic Agatha Raisin] and when you're leading a show, you're there because people want you there. How the day goes is down to you, to a great extent. Your mood and behaviour infect everyone else on the set.

"It's a responsibility – and it's not a responsibility I could have coped with when I was younger. So I'm grateful it's happening now. For me, it's about the here and now."

So Jensen won't be drawn on her longer-term future on Shetland? "I never look too far ahead," she smiles. Still, something tells me that the forecast will be sunny.

Shetland season 8 airs on Wednesday 1st November at 9pm on BBC One and iPlayer. Ann Cleeves's Shetland novels are available to buy now.

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