LONG before Ashley Jensen became a household name thanks to Extras, Ugly Betty or Catastrophe, there was a lesser known role in a touring production called Drink, Smoking and Toking.

The poignant, coming-of-age tale – set in deepest, darkest West Lothian – was written by my then 15-year-old brother as part of the 1996 Royal Court/Marks & Spencer Young Writers' Festival.

Jensen played a Mean Girls-style, older sister called "Susan" who mercilessly teased her younger sibling.

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There's a gasp and a hearty laugh from the actor as the penny drops. "Oh my gosh, I played evil you," says Jensen. "That is so funny."

I can still remember sinking lower into my seat at the Macrobert Arts Centre in Stirling, cheeks burning with embarrassment, as I watched Jensen portray my bad self on stage. Reader, let it be stated for the record I wasn't that terrible a sister as a teenager. Was I? Erm …

Returning swiftly to the present day, Jensen is here to talk about new BBC drama Love, Lies and Records which sees her return to our television screens this week.

The six-part series, written by Band of Gold, The Syndicate and Fat Friends creator Kay Mellor, is set in the offices of a births, deaths and marriages registrar. Jensen plays newly promoted Kate Dickenson who is torn between growing work demands and being matriarch of a 'blended' family.

The 48-year-old actor clearly relished the role, speaking highly of the way in which Mellor fleshed out that world. "Kay writes brilliantly for women and in a very honest, sometimes slightly uncomfortable way. She taps into humanity," says Jensen.

"Her characters are not spies or amazing doctors; they are just ordinary people getting on with their lives. Because this show is to do with births, marriages and deaths, all of us have to deal with one – or all of those – at some point in our lives. So, it is eminently relatable."

According to the BBC blurb, the series "explores how women in particular have to juggle their lives". Some people may roll their eyes at what sounds like a slightly hackneyed concept, but we're talking Kay Mellor here. I'm envisaging it is a touch cleverer than that?

Jensen certainly believes so. "I think because she writes so honestly. She is not taking a standpoint. It is a reflection on real people with struggles.

"Nothing is particularly cut and dried. Nobody is black and white. There is no baddie and there is no goodie. It is just honest people trying to get on with life. Hopefully that is what will be relatable."

Jensen, who hails from Annan in Dumfries and Galloway, was first catapulted into the public consciousness with her breakthrough role as socially inept Maggie Jacobs in the Ricky Gervais comedy Extras in 2005.

Her star continued in the ascendant when she was cast in hit US sitcom Ugly Betty alongside America Ferrera which, set in the cut-throat world of a fashion magazine, ran for four series.

In more recent years, Jensen has had parts in Robert Carlyle's directorial debut The Legend of Barney Thomson, dystopian black comedy The Lobster with Colin Farrell and as lovable amateur sleuth Agatha Raisin in Sky 1's murder-mystery series based on MC Beaton's books.

Other career highlights include voicing characters in big budget animated children's films such as Gnomeo and Juliet, Arthur Christmas and How to Train Your Dragon.

She has given us plenty of laughs as Fran in award-winning Channel 4 comedy Catastrophe, the neurotic, awful friend of lead characters Sharon and Rob (played by the show's co-creators Sharon Horgan and Rob Delaney) and ex-wife of Chris (as brilliantly depicted by fellow Scot Mark Bonnar).

A fourth series is in the pipeline – "I will be filming that at the end of the year" – and Jensen says she feels incredibly lucky to be part of a TV show that has garnered such cult status.

"What is interesting about Catastrophe is that everyone is a little screwed up and slightly unlikeable," she says. "Even the heroes are fallible. Everyone is fallible. I think that is what makes an interesting character. It's not like your obvious hero in the conventional sense of the word.

"What they seem to be able to do is get an audience to actually give a s*** about the characters. I ask people: 'Do you really like Fran?' and they say: 'I do! I mean I kind of hate her, but I feel sorry for her …' That is a real testament to their wonderful writing."

Many of the one-liners are eye-wateringly close to the bone. How are the cast not constantly corpsing? "Oh, we do," says Jensen, before adding that Catastrophe reminds her of the great fun she had filming Extras with Gervais. "We do have a laugh, it has to be said."

Although the most recent series was tinged with sadness too. Shortly after Carrie Fisher, who played Rob's mother Mia, wrapped filming last December she suffered a major heart attack on a flight from London to Los Angeles. Fisher died a few days later at the age of 60.

The scenes in Catastrophe marked her final performance. Jensen says that all of the cast and crew were hit hard by news. "The first time I had met her was last year just before Christmas because we had never been in the same scenes before," she says.

"We were filming Sharon's dad's character's funeral. I had the most wonderful morning just listening to her. She wasn't like some of these people who just talk and you listen – she was happy to listen to other people as well. I feel really privileged that I got spend a morning with her.

"Then within a week she was dead. It was just so shocking. She was such an amazing part of the show."

Jensen recounts being at the Attitude Awards with Horgan and Delaney in 2014 when the idea to approach Star Wars actor Fisher – who was also among the guests – was first mooted.

"I think that's where they thought: 'What about Carrie Fisher?' They basically asked her thinking: 'We won't get her' and then they got her. Everyone was like: 'Oh my God, we have got this Hollywood legend in a British sitcom and she is amazing.'"

Jensen is based in Bath where she lives with her actor and writer husband Terence Beesley, 58, and their eight-year-old son Frankie.

"I was in America for six years," she says. "I bounced into London and thought: 'I'm not sure I want to bring a child up here.' Not that there is anything wrong with London, because I love London, but living in America there is so much more space.

"To be honest, I didn't have the £14m to buy that amount of space in London. So, like a lot of people do, we moved out. My son is able to run about in fields and climb trees here which is like what I had growing up in Dumfries and Galloway, a more rural upbringing."

She regularly returns home to Annan to visit her mother Margaret (in fact, when we speak, Jensen is heading there the next day).

Her mother, who worked in a school for children with learning difficulties, was a single parent (Jensen has no contact with her father).

"I look back and realise how brave she was as a parent to have let me pursue what I wanted to do," says Jensen. "There was never any doubt about what I wanted to do. I always knew I wanted to do this. I don't quite know where it came from.

"I used to do little daft radio shows when I was wee and put on funny voices. I would interview my mum and she is so not actory at all. I was always quite single-minded about what I wanted to do.

"She let me go to the National Youth Theatre and I look back now and think: 'What a brave thing for my mum to let her 14 or 15-year-old daughter go down to London'. I've since spoken to her about it and she said: 'Yes, I thought it might put you off'. Of course, it didn't, clearly."

Rather it merely strengthened Jensen's resolve. "I felt I was amongst people who wore kooky clothes like me and did funny voices and I suppose were quite extrovert and relatively confident, but from all different walks of life," she says.

As a teenager, Jensen wore glitzy Doc Martens and carried a kettle for a handbag. That may not have stood out quite so much in London, but in Annan?

"People occasionally used to go out just to see what me and my friend – who subsequently went to art school – were wearing on a Saturday night at the rugby club."

They were the talk of Annan? "I think we were the joke of Annan to be honest. I look back and think about the purple lips and the kettle handbag and the sprayed glitter Doc Martens … Things like that are quite cool now, but in 1983, it was a bit weird."

I'm curious what first drew her to acting? "Coming from a small, rural farming market town, culturally there wasn't much going on there. It wasn't one of these things where travelling troubadours and theatre came to the town and I was influenced that way.

"For me, it was basically sitcoms from the 1970s and the main one being Some Mothers Do 'Ave 'Em and Frank Spencer. It was that which drew out my passion. I think [Michael Crawford] is genius. I show it to my son and he laughs too. The timing and physical comedy still stands today."

Jensen spent six years living in Los Angeles, yet starting her career that wasn't even on her radar. "I never ever had ambition to go to America. That was never on the cards. My ambition was much more than that. It was basically to sustain and support myself as an actress in my chosen profession.

"The things that have happened are beyond my expectations. I never imagined that I would live in Hollywood and be nominated for Emmys and have security guards with half a million pounds worth of diamonds and a limousine waiting outside.

"To be drinking Champagne from a magnum on the table as you queued behind Drew Barrymore in the toilets. We had to pinch ourselves sometimes when we were in America.

"But I was old enough and Scottish enough to know that it wasn't forever. The one thing that LA taught me is that show business is called show business" – she emphasises the latter word – "and it is a business. When you are in the hot show, you are hot for that period of time. Frankly, I didn't want to grow old there."

When we speak it is August and Hollywood is yet to be rocked by the sexual assault allegations against Harvey Weinstein (which the film mogul has "unequivocally denied").

Jensen and I discuss the issues of gender parity within the industry. A recent study reported that the amount of dialogue women get in Hollywood films decreases after age of 40.

"I think we are aware of it now," she says. "It was a taboo where no one even talked about it. The thing that upsets me is that women are not allowed to get old.

"There is this whole insidious, subtle thing that women are having to do stuff to ourselves to try and maintain some form of youth. It is not a great message to be sending to anyone. It is kind of sad and quite frightening as a woman to be in the industry and to have that."

Jensen – who recently said that it was "becoming more normal to see a face that looks like a cross between a hard-boiled egg and a cat" – counts herself as fortunate not to have been at the sharp end of that perfection-driven obsession during her time in the US.

"It is weird because people used to say to me: 'Were you pressurised in LA?' and I was never pressurised. Maybe it is because I was in comedy and played the best friend, so there wasn't quite that pressure to look a certain way.

"Maybe it is because I was never really a leading lady. I'm not doing a false humility here, but I was never the best looking girl in the room. I was never the worst looking girl, but I think there is more pressure when you have been beautiful at 25 to try and maintain something. I was never that.

"My gran used to say: 'Aye, don't get too carried away with your own self-importance.' There is that feet firmly on the ground scenario with being Scottish. I don't know whether it was with being a little bit older because when I went over there, I was in my late thirties."

The ubiquitous nature of cosmetic procedures is something she is acutely conscious about. "I feel more pressure, weirdly, 10 years later now I'm back in Britain. It seems much more prevalent. People on UK television are doing things to their faces and you think: 'Oh my goodness …'"

Jensen wouldn't have anything done herself? "It's not for me. Someone has to play the old people, haven't they? They will be about three of us left in 10 years' time that actually look our age.

"I have known of someone who couldn't ultimately be employed because she'd had so much work done to her face and didn't look an ordinary, 50-year-old housewife. Although I suppose some ordinary women are doing it now, which is where I think the pressure is coming.

"It is not just about: 'Oh, I want to try and maintain my youth'. It is a huge cultural movement. The bottom line is basically saying that women are not allowed to get old and that is what annoys me."

Jensen, who did an acting degree at Queen Margaret College in Edinburgh, isn't one to rest on her laurels. She recalls honing her craft as a young actor while criss-crossing the country with shoestring touring theatre productions.

"You would put the set up, do the show, take the set down, get in the white van, travel to the next place, sleep and do the same the next day for four months in a show about Christmas, that didn't mention Christmas, which meant they could eke it out until March.

"I feel as if I have really served an apprenticeship. I wouldn't have it any other way. It gives you an appreciation. I still don't take anything for granted."

Although these days Jensen is in a strong position to pick and choose her projects. "I get offered quite a lot of stuff and I'm quite discerning about what I do," she says. "I don't just want to work all the time for the sake of working. Is it wrong to say that?

"There is a balance. I have got a wee boy and I want to be part of his life and not just always working. I don't want to saturate myself too much on television so that people become really p***** off at the sight of my face and say: 'Not her again'.

"The only power an actor has is to be able to say no. I'm in a position at the moment where I can say no to stuff and wait for something to come along that I do feel passionate about."

Love, Lies and Records begins on BBC One, Thursday, 9pm