“That was my shoes, not my bottom,” says Tamsin Greig, after emitting a squeaky-squelch in a back room at the Royal Opera House. “I mean, I would tell you if it was my bottom.”

In person, the Friday Night Dinner star has such a concentrated stillness and seriousness about her that she catches me deliciously off guard every time she says something funny. Which she does often in the hour we spend together discussing her new (speaking not singing) role in the Royal Opera’s new production of Donizetti’s 1840 comic opera, La Fille du régiment. It’s a kind of magic trick, the way she fixes you with her small, dark, compassionate eyes, nods in slow motion, seeks out the deeper meaning of my questions… then a joke or rare F-bomb will pop out of her like a rabbit from a hat.

It’s a sweetly subversive, self-generated version of what she has done so brilliantly in her most famous sitcom roles – often playing the more “normal”, relatable and empathic character in a cast of eccentrics, trying to hold herself together as situations become increasingly chaotic around her. In Bafta-winning Black Books she is the city shop owner turned temp battling to control her neuroses and bring calm to the more unhinged characters.

In Green Wing, she played the new doctor struggling to make sense of the bizarre behaviour of her new colleagues. In Friday Night Dinner, she was doting Jewish mum Jackie, relentlessly pleading with her family to sit nicely for her “crimble crumble” as slapstick anarchy unfolded around her.

On stage, Greig brought tears to audiences’ eyes in her Olivier Award-winning turn as Beatrice in the Royal Shakespeare Company’s 2006 production of Much Ado About Nothing, and was equal parts ludicrous and pitiable as a cleverly gender-swapped Malvolia in the National Theatre’s 2017 production of Twelfth Night. Meanwhile, in her long running role as Debbie Aldridge in BBC Radio 4’s rural soap opera The Archers, she regularly brings a welcome edge of crisp wit to the gentle meander of events.

Greig as the Duchesse de Crakentorp in ‘La Fille du régiment’ at the Royal Opera House (Photo: Tristram Kenton)

“Sets and theatres can be absolutely exhausting,” says Greig. “Or at least, I get exhausted. I have to make it absolutely clear that if there’s a lunch break I will eat for 10 minutes and then I’ll be unconscious for half an hour. Then I can get on and cope with the rest of the day.” She sips a herbal tea and smiles. “I’ve had to have a little bit of quiet time before this interview. Because all the amazing sets and music, the gorgeous costumes and wigs in this opera? It’s like being on a Spielberg set.”

Greig was, she says, “a power napper from childhood”. She was born in 1966 in Maidstone, Kent – the second of three sisters, dad an industrial chemist and mum had a flare for am dram. She was raised mostly in a loving but dilapidated home in Kilburn, north-west London, she has affectionately described as “a shithole”. She adds: “I can remember falling asleep while my mum was carrying me somewhere. I can’t think why she would have agreed to give me a piggyback but I remember the feeling of waking up and being unable to move because that’s an odd position to sleep in and all my muscles had crumpled up.”

Opera was “a world I had no experience of, growing up. I turn 60 this month and I only saw my first opera last year. Madame Butterfly. It was breathtaking.” Though money was tight, the family saved up every year for the ballet at Christmas and Greig’s earliest ambition was to be a ballet dancer. “There was no way I was ever going to make it as a ballerina,” she says. “I’m too tall” – she’s only five foot six, although her slim frame and spiky hair make her seem taller – “and I didn’t like the pain in my feet.”

She shrugs. “I have deep awe for dancers who can override the pain… For their athleticism and drive and the deep beauty of being in their bodies, living through every fibre of those bodies. It’s extraordinary.” She pauses, sips and adds that, “as actors, we’re doing something extraordinary in our own way. It’s weird.”

Because Greig once described herself as a “high-functioning introvert”, I’m curious about where her own drive to perform comes from. Would the classmates who knew her at seven, eight, or nine guess she’d end up on TV? Famous? “I don’t know,” she mulls. “I have been described in some interviews as the sort of the classic middle child who needed attention, which I find disappointing as a diagnosis. Because there was space for me.”

In ‘Friday Night Dinner’ with Paul Ritter, Tom Rosenthal and Simon Bird (Photo: Mark Johnson/Channel 4)

Greig balances a calculated efficiency with her artiness. She’s one of very few actors I’ve met with a maths A Level (along with English and French). After graduating with a first-class degree in English and drama from the University of Birmingham, she made the practical decisions to take a secretarial course to keep herself afloat between roles. Her own experience of temping fed into the much memed scene from Black Books in which her character Fran Katzenjammer sits awkwardly at a desk in an open plan office and repeatedly types “what am I doing here?” into her computer in an effort to appear busy.

Because my kids loved Friday Night Dinner so much, we watched Green Wing together as a family when, I admit to Greig, they were probably a bit too young. As a mum of two sons and a daughter (born between 1999 and 2005) she winces. “Yeah, there was a lot of sex in cupboards and stuff.” A shrug. “Maybe the best way to teach them. It’s either that or porn. F**k it.”

At the time, Greig says she had no clue that Black Books and Green Wing would become comedy classics. “Especially while I was filming all those scenes where I took ages walking down the corridor in Green Wing – I had no idea they were going to do that brilliant editing, speeding things up.

“We had no idea what we were doing. But we had so much fun. And it was great to be part of this breeding ground for interesting actors. Although we were still not as diverse as we could have been.”

She’s funny about her time in LA filming Episodes with Stephen Mangan, although she refuses to be drawn on the culture differences between the UK and US entertainment industries explored by the show, which is about British sitcom writers working in Hollywood, “because it’s a can of worms, isn’t it?” A pause. “You know what I mean? Everybody’s ego needs to get knocked about a bit but it’s death by encouragement out there. It’s just absolutely nonsense. And so you learn to be incredibly discerning. Or take it all with a beautiful pinch of comic salt, which may well be sugar in America.” Wouldn’t she prefer British salt to American sugar? “Both will kill you.”

From left, Greig as Fran Katzenjammer, Dylan Moran as Bernard Black and Bill Bailey as Manny Bianco in ‘Black Books’ (Photo: Channel 4)

What does she make of Hollywood star Timothée Chalamet’s recent assertion that “nobody cares” about art forms like ballet and opera any more? “Everyone’s entitled to their opinion,” she says. “It’s intriguing he would say that, since his mother and his sister are both trained ballet dancers. It will take more than Timothée Chalamet to kill the opera.”

Although Greig is “a mix of nervous and excited – nervecited” about her Royal Opera debut, she’s at an age where she’s able to enjoy the process. She knew she’d be taking the part of Duchesse de Crakentorp as soon as she visited the “beautiful” opera house and watched a video of Dawn French in the role in 2007. “I’ve always been good at saying no to projects when I couldn’t hear the music in them,” she says. This time the music will be real, and orchestra-sized.

La Fille du régiment is about a foundling girl adopted by a group of French soldiers – her 1,500 “fathers” must be convinced to consent to let her marry her sweetheart. “It’s problematic, from a modern standpoint, that our heroine is a possession,” says Greig. “But her character – as a potty-mouthed tomboy – is quite subversive. And the opera asks good questions about nature and nurture that challenge the class system. I think we, as artists, are here to upset the status quo. We should not be sleepwalking through the world. We should be asking: how can we unsettle this day?”

Before I leave, I ask if Greig would mind posing for a photo with my 16-year-old son, James. He and my daughter are such big fans of Friday Night Dinner, they ape the sibling rivalry of Jackie’s adult sons and are listed in each other’s phones as “Pissface” and “Pussface”.

“Which one are you?” Greig asks. “Pissface,” he grins, sheepishly. “Thought so!”

‘La Fille du régiment’ is at the Royal Opera House, London, until 24 July