RONNI Ancona is in full flow, shifting seamlessly between the brisk, clipped tones of Olivia Colman to the husky drawl of Jennifer Lawrence and then the distinctive cockney accent of Paloma Faith.

We’re reminiscing about her time on The Big Impression – the BBC comedy series which made her a household name celebrates its 20th anniversary this year – and the Scottish actor is rattling off a list of her favourite modern-era celebrities to parody.

“I don’t care what anyone says about there being a lot more women on TV, it is difficult to find distinctive voices because women in broadcasting still kind of have to be the girl next door,” she laments.

We’ll come back to that in a moment. First, we’re here to talk about her imminent return to our screens in the BBC drama, Last Tango in Halifax. Ancona plays the odious Judith, a high-functioning alcoholic who wreaks havoc yet, ultimately, is deeply damaged herself.

It’s been a smidge over three years since the show last aired – a 2016 Christmas Special – and much has changed for Judith who, according to Ancona, has “literally become richer than JK Rowling” after coining a bestselling book series.

For those unfamiliar with the magic of Last Tango in Halifax, it centres on the romance between widowed septuagenarians Alan and Celia – played with aching brilliance by Sir Derek Jacobi and Anne Reid – and has a cast that includes Sarah Lancashire and Nicola Walker.

The premise is based on the real-life experience of the show’s creator Sally Wainwright whose mother Dorothy lost contact with a childhood friend, Alec, at 15. The couple reconnected on the social networking website, Friends Reunited, 60 years later and within six months were married.

Last Tango in Halifax has been hailed as a triumph against ageism, with its unflinching depiction of Celia and Alan’s relationship, in all its joys and foibles, proving a hit among viewers. Ancona is in wholehearted agreement with this synopsis.

“For a long time, when older people were portrayed in things, they were rocking under crocheted blankets,” she says. “Or reduced to stock characters who were not sensual, not attractive, and not multi-dimensional, they were just ‘the old people’. They were marginalised.

“That is so wrong because people don’t change that much. Sure, they get older and physically become more infirm, but they are, in essence, the same person they always were. What is clever with Last Tango in Halifax is that it portrays a couple – Celia and Alan – as very sensual and attractive, and why shouldn’t they be? I think it hit a chord with people. And, to me, it reaches right across the demographic.”

Ancona is warming to her theme. “There is so much TV now where it is ‘this is for middle-aged people’ and all the cast are middle-aged or older. Then you have all the culty Channel 4 shows where everybody has to be young.

“Obviously, there is a place for that. But for large swathes of the public, they don’t recognise it. I hate the way TV has become. Everything has to be youth-oriented or, equally, it has to appeal to Doreen from Leeds.”

Playing Judith takes a special knack, as Ancona can attest. “I was counting it up the other day and apart from a couple of scenes in the Christmas Special, in all honesty, there are only a few scenes where she has been sober. I have a horror of doing bad drunk acting. It is quite difficult to pitch tonally doing drunk.”

Ah, the fine line between intoxicated exuberance and hammy hammered? “There is a tendency to do drunk as being very slurred,” says Ancona. “When, actually, people who are inebriated articulate even more because they are conscious of making other people aware that they are not drunk.

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“Judith is a functioning alcoholic. There is a scene in the series where she is supposed be doing something extremely important, a lot of people are relying on her and she is basically half cut.

“Everyone is really worried about her, but often functioning alcoholics can rise to the occasion and it’s not a question of them just falling over all over the place. That is the cliche. I was determined to make sure I played the truth.”

I’m curious why there’s been a long hiatus. “A lot is to do with Sally being such a genius and so prolific,” says Ancona, referring to Wainwright’s work on dramas such as Scott & Bailey, Happy Valley and more recently Gentleman Jack.

“Also, I think Sally wanted to leave enough space to see how the characters could develop in terms of coming back to them and seeing what has happened in their lives. That worked to my advantage because Judith has become richer than JK Rowling.

“She has come out with a book series about a female Robin Hood character. They have become unbelievably successful. The only thing I could possibly compare it to, it’s like a much more sophisticated, erudite version of The Twilight Saga.

“That is another thing that Sally has done quite cleverly. She could just have made her a chick lit writer who comes up with the new Twilight Saga, but what Judith has done is written books that are eloquent, intelligent, punchy, feminist and very zeitgeisty.”

Although, as Ancona reveals, this newfound success has done little to sate the ever-present demons. “Judith falls off the wagon and her old habits return,” she says. “Now she is drunk and rich, a deadly combination.”

While character acting is another string to her bow, many people still know Ancona best for her comedy work. Last year, she joined forces with Lewis MacLeod – known for Dead Ringers and Newzoids – to take their show, Just Checking In, to the Edinburgh Festival Fringe.

At its heart is a once-glamorous (fictional) Scottish hotel being sold to Donald Trump. An army of eccentric staff and celebrity guests conspire to halt the sale. Ancona and MacLeod voice everyone who has passed through its doors over the years.

“Everybody slightly seizes control and we lose ourselves in it,” she says. “That did well, and we are going to take it to the Soho Theatre.”

She has several more ideas. “I am doing a couple of big projects with Sally Phillips. One is about Palm Dog, an award given to the best canine performance in film. Last year Sally and I presented it to Quentin Tarantino [for Once Upon A Time In Hollywood].

“We are doing a film about that and another project for TV. Then I’ve got something that I am doing with Morwenna Banks that is hopefully going to become a film. I have been doing stuff with Alistair McGowan as well. All sorts of bits and bobs.”

She performed a series of sketches and impressions with McGowan for the debut live edition of Gaby’s Talking Pictures, earlier this month. The BBC Radio 4 panel show presented by Gaby Roslin is doing a residency at Leicester Square Theatre in London.

“It has been perfect because it is the 20th anniversary of The Big Impression,” says Ancona. “We wanted to do some stuff together, but we didn’t want to commit ourselves to a big thing and I’m sure people wouldn’t particularly want us to do it anyway …”

I bet they would, I enthuse. “Maybe I’ll come and talk to BBC Scotland about it. That’s not a bad idea. Because we have all the clips and I want to do something about how celebrities change.”

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Ah, yes, the heady days of the early noughties when the showbiz landscape was starkly different and those who inhabited it remained largely distant, untouchable creatures. No one was Instagram famous and Kim Kardashian West had yet to break the internet.

“When we did that show, nobody had social media,” she says. “It was fun to parody and spoof things and imagine scenarios for Posh and Becks. Now you can’t do that because everything is so transparent. As a consequence, it is quite hard – everybody has become a parody of themselves.”

The Big Impression became must-watch viewing during its four-series run on BBC One between 2000 and 2003. “We were very lucky because we had free rein,” says Ancona. “I remember having a great time doing the Big Brother characters. We did the Royal Family as The Royle Family.”

Who did she enjoy impersonating most? “Posh and Becks were fun to do. I used to do a lovely Nancy Dell’Olio and Nigella and the characters from Friends.”

Fast forward two decades. Does Ancona have a modern-day favourite? “I have become obsessed with doing Olivia Colman,” she says, demonstrating her technique. “Only ever says things in two words, very quick. ‘Philip, look after, the corgis.’”

Hours of work can go into nailing an impression. “You need to watch clips of a person in so many different guises. Then you can decide what is a constant factor and what isn’t.

“I did a little bit of teaching Renee Zellweger on the film Judy. That was quite fun.” Ancona pauses, before hastily adding: “Not that she wouldn’t have been totally brilliant without me. Please don’t write that down as, ‘it was me who won the Golden Globe’. That would be bloody awful.”

Testament to her perceived place in the comedy pecking order, Ancona mentions doing the quiz show, Pointless, with her good friend and fellow impressionist Jan Ravens. “All the impressionists are very close. We’re the pariahs of the comedy world. We are one rung down from ventriloquists.”

It was while studying design at Central Saint Martins in London (she left Scotland at 17) that Ancona cut her teeth as a performer. “I had always wanted to go into comedy. When I was at art school they would put on these lavish productions because there were some brilliant designers.”

Ancona began honing her craft doing stand-up comedy and improvisation. Although not without some bumps in the road during those early days.

“I was a terrible compere,” she says. “I used to compere at this club on the Thames called the Tattershall Castle. Oh my God, talking about how long ago this was, a typical bill would be Eddie Izzard, Lee Evans, Jack Dee and Jo Brand.

“It was the golden age of the circuit. I look back now and it was just extraordinary. I did well when I came out on my own [as a comedian] and not as a compere. I won the Time Out Hackney Empire New Act of the Year in 1993.”

I imagined Ancona was going to tell me she got a taste for the stage when her artist mother painted sets at the Gaiety Theatre in Ayr. “Aw, well actually, that was a huge influence,” she insists. “Ironically, I trained as a scenic artist as well.”

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Certainly, a seed was planted in her formative years. “I used to get to meet all the panto stars like Jack Milroy and Rikki Fulton and Mary Lee. I loved pantomime. I’m sure this isn’t a very trendy thing to say but Scottish pantomime had a huge influence on me. I adored it, the Scottish humour.

“People talk about Irish humour a lot, but I think Scottish humour is very interesting. Scottish women are some of the funniest I have met in my life. I remember going to Glasgow and working with an English actress. She said to me: ‘Is it normal for all Scottish women to be so funny?’”

She’s fiercely proud of her Scottish roots and a childhood spent in Troon. Ancona was born in Louth, Lincolnshire, and arrived in Ayrshire at three days old. She frets when I mention this. “I was supposed to be born in Scotland,” she clarifies. “We were on our way up to Scotland when I was born.”

I’ve clearly struck a nerve. “I never really like to talk about being born in Lincolnshire, do you know what I mean? My mum’s family all come from Kilmarnock.

“I have cousins in Edinburgh, Glasgow and Stirling. My parents don’t live in Scotland any more, sadly, but they miss it horribly. My mother was very traumatised by leaving Aberdeen. They went up to Aberdeen after Troon. My mum loved it. I don’t think she has ever got over leaving Scotland.”

Later, clearly still worried about her Scottish credentials, she adds: “I’m ashamed to say I got a question wrong on something about a Rabbie Burns poem and literally burn with shame every time I think about it. It is too awful. I’m worried I might be disembowelled like William Wallace.”

We move on to talking about her family life. Ancona is the youngest of three children. Her father was a commander in the Royal Navy. “My brother made it to admiral,” she says. “My other brother is a car designer and has just designed the latest London cab, the electric one.”

Stretching further back, her roots can be traced to Italian-Jewish descent. “Quite a long way back,” she says. “I’ve read somewhere you can get your Portuguese passport if you can prove your Sephardic roots. I thought that would be a good project.

“If Scotland does get independence, I’m now a bit worried about the Lincolnshire thing. I might have a wee bit of a problem due to those three days,” she says, laughing heartily.

Has Ancona done much genealogy? “My father got into it. If you have quite an unusual name – which we have – it is easier to do. We discovered that we had married into the Montefiore family.”

She has fond memories of living in Troon. “Lots of walking around the dunes. Me and my friend Audrey collecting [juice] bottles to get a refund. The taxis coming down from Glasgow with the school kids and all the cabs decorated.

“Working at the Open. That was amazing. You would get wee bits of jobs. I remember every house in Troon would take a golfer in. One of my first memories is this small, Belgian, rather rotund, golfer who came to stay at our house. He would run around in his underpants.

"I remember him giving me a box of Terry’s All Gold chocolates. That was off the scale. In those days, the concept of affluence was if somebody had a SodaStream. I still remember this box of chocolates because of the shock of me being given them.”

Today, Ancona is based between London and Oxfordshire, where she lives with her husband and their two daughters. She laughs wryly when asked about her passions outside work.

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“I have two girls I adore, and in the loveliest possible way, children are demanding. It is like being a PA to two A-listers. I have a 14-year-old and a 12-year-old. That is pretty full on. The spare time I have I like to go for walks and do stuff with the kids. Does that sound desperately dull?”

Ancona is part of the so-called “sandwich generation”, caring for her children and ageing parents alike. “When I do get any time to myself, I just collapse in front of the telly and watch a box set.”

We can all relate to that. Pass the remote.

Last Tango in Halifax begins on BBC One, tomorrow, at 9pm. All previous series are available on BBC iPlayer