In the beige blandness of a Granada TV meeting room, Rachael Stirling looks as out of place as a flamingo in a suburban pond. Dressed in a tailored black suit, she’s all coltish leg movements and hyperactive conversation. “I’m an absolute motormouth. Forgive me.”

During our meeting, conducted through clouds of cigarette smoke and in the kind of accent that could easily mark her out as top Tatler totty, her favourite words include “divine” and “adorable”. There again, she is also quite fond of “f***” and “w*****”. She’s Audrey Hepburn with a touch of builder thrown in — she is also hugely likeable.

While filming Five Little Pigs, the first in a batch of extremely good new Poirot mysteries, the 26-year-old actress and daughter of Dame Diana Rigg proved her appeal by forging some “divine friendships” with the ensemble cast. “Me, Julie Cox and Aimee Mullins (her female co stars) were nicknamed the Frascati Sisters. We were all staying in a pub in Stevenage and in the evenings the three of us would sit in the garden and drink litres of white wine.”

The two-hour period drama, scripted by the playwright Kevin Elyot, is the story of a society murder. Stirling’s character (Caroline Crale) is hanged for poisoning her husband, Amyas (played by Aidan Gillen). Years later, Poirot (David Suchet) sets out to prove her innocence, revisiting the crime through the eyes of the five other potential suspects. Though set in the cut-glass world of the English upper classes, it’s a rather dark tale of dysfunctional relationships.

“For me, Agatha Christie was a genius who wrote these five broken characters who feel absolutely true,” says Stirling. “But to achieve that truth we all had to go to the dark centre of the people we were playing. Though, of course, I sound like such a w***** saying that.”

In fact, she sounds like an actress who is never less than passionate about her work, in particular Tipping the Velvet, the BBC’s Sapphic drama in which she starred with Keeley Hawes. She did it knowing full well that there would be a fuss. “I mean, I’m not thick. I did suck Keeley’s nipples and appear naked, covered in gold paint and wearing a dildo. But the outrage overshadowed what was a brave and witty piece of work. In America they applauded it as an original drama. But here everything has to be reduced to a tabloid level.”

The British response (one letter-writer drew the outline of his penis on a piece of paper with the words “actual size” written by the side) was enough to drive Stirling into a seven-month self-imposed exile from the screen. “The fact that every script I received after Tipping the Velvet had the words ‘she gets her tits out’ by page four didn’t exactly help,” she says. “And while I’m not averse to scenes like that, even if they do often involve you being naked and feeling very foolish in front of 60 fully dressed people on a set, I did think: ‘Right, time to step back and wait for the right thing to come along.’ And I’m very glad I did.”

She was backed by her “muma” both during and after the furore. Comparisons between the two women have always been onerous to Stirling. “How can you compare a green 26-year-old to a very experienced actress at the peak of her profession?” she asks. “It does neither of us any favours.”

For all that, she admits that the mother-daughter relationship now benefits from a mutual professional respect, with each able to criticise the other’s work. Growing up, Stirling was only vaguely aware of her mother’s fame and status. Rigg was not only the leather-clad Emma Peel, but also one of the most highly regarded actresses of her generation.

“I do remember people pointing at her when we were in Marks & Spencer. But, really, she kept work and home very separate, so I knew very little about the business. On my first film, Still Crazy, they told me I’d ‘wrapped’ and I hadn’t a clue what they meant. So I sat in my caravan until they came round to lock up. It was pretty tragic.”

Stirling had won the role while still at university. She had already cut her teeth in National Youth Theatre productions and in plays at Wycombe Abbey boarding school in Buckinghamshire. “I found acting a wonderful retreat from my feelings of homesickness at school.” It was, she says, a time of great innocence. “When we had discos with the local boys’ school no one asked me to dance, probably because I just wasn’t very attractive.”

She’s a swan now, of course, and could have her pick of the boys. A couple of months ago she ended a two-and-a-half-year relationship with John Lycett-Green, a DJ who is also John Betjeman’s grandson. Instead, she is blissfully single, a state that suits her current schedule. She admits that a potential beau might suffer by comparison to her rather colourful father. Once married to Princess Alice’s niece, Charmian Scott, Archie Stirling followed divorce to Rigg with a third marriage to Sharon Silver.

“I don’t think I’ve got a dad complex,” Stirling laughs. “But I do worship him. He’s wise, funny and divine. The qualities I suppose I would look for if I was going to fall in love.”

For now, however, romance is reserved for roles such as the one that she is currently playing in A Woman of No Importance at the Theatre Royal, Haymarket, in London, where the portrait on the facing page was shot. “But it’s not all romantic heroine parts.”

Take the forthcoming Freeze Frame, a low-budget British movie in which she stars with Lee Evans. Devoid of any romance, it is a dark piece about paranoia. Stirling plays a reporter investigating a murder that Evans’s character may have committed ten years before.

“In one scene, I have to obtain a sample of Lee’s DNA by rather violent means. It involves a rope, a gun and a rape . . . his,” she smiles.

At least this time there’s not a dildo in sight.

Five Little Pigs, Sunday, ITV1, 9pm

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