There is something meticulous about Helen McCrory, and it’s not just the way she eats her macaroni cheese so neatly, or her titchy ballerina frame, or even the perfectly timed gusts of charm that have us all giggling like fifth-formers around a prefect before the interview has even started.

Discreetly, as the assistants leave, she passes me a napkin and quietly points out that I have smudged black ink from my pen across my face, which is now bleeding into my mouth and across my chin. “Up a bit, just a little bit more,” she encourages, in that honeycombed voice. “Keep going, almost. Other side, yes I think that’s it.”

^{(Left - right) Sophie Rundle, Helen McCrory, Cillian Murphy and Annabelle Wallis at a gala screening of Peaky Blinders (PA)}

Meticulously polite, funny and glamorous. Meticulously everything. A hoot. Make her head girl now. And it’s not that McCrory is without any smudges. It’s just these are perfectly judged. For all the recent red-carpet snazz, I’ve bumped into her on Hampstead Heath, Ugg boots pulled high and hat pulled low, the morning after the Martinis. Meanwhile, the critics go giddy, calling her “totally compelling”, “wildly charismatic”, “the imprinteur of excellence”. It’s tempting, just for the sake of originality, to find a chink, but she’s been so lovely and she’s stopped me looking like a fool.

Also, at 45, McCrory has become the poster girl for grown-up women: beautiful but un-Botoxed; complicated but funny; clever but open. It comes as little surprise then, that she was first choice for the powerful, but vulnerable, matriarch, Aunt Poll, in the epic new BBC Two series, Peaky Blinders.

^{Helen McCrory as Aunt Polly Gray in the Peaky Blinders}

Set in the ganglands of 1919 Birmingham, the series features racketeers, communists, mobsters and sadistic police vying for their slice of a post-First-World-War future against an industrial backdrop and a Nick Cave soundtrack. McCrory shares top billing with Cillian Murphy, who plays her gang-leader nephew, and Sam Neill, the maniac Belfast police chief brought in to control the mayhem.

“A lot of British period drama is either about a certain class or told in a certain way,” says McCrory. “This is a very different approach to a very powerful story. A huge echelon of society fought in the First World War and did not come home to the hero’s welcome they hoped for. Far from it.

“It’s about those people trying to come to terms with a war that brutalised them, because what happened to them wasn’t left in the fields of France. They brought that hell home and, in turn, brutalised those around them, including the women like Aunt Poll. It’s about how betrayed people felt and how out of control.”

Certainly there are few parasols, but neither is this stock-in-trade “gritty social realism”. Instead Peaky Blinders has been dubbed a period Blade Runner: dystopian, stylised and influenced by American gangster movies and Westerns. Men in peaked caps lined with razors – the “peaky blinders” – make their way through blackened streets and skim their hats across the eyes of anyone who tries to cross them. Morality is blurred. Power is violence. But McCrory is quick to point out that it is also a story about women. Aunt Poll’s first entrance, pistol in one hand and hatpin in the other, is one of the most striking opening images.

“I loved this opening,” says McCrory. “It takes you into a completely different view of women at this time. Did you know that police were called out more often for fights between women than men? They controlled every last detail of domestic life. Each street would have a matriarch who decided what day washing day was, and who got the water in what order. If you were last on her list, you got the dirty water. Not a woman to cross. These were also the women who had held everything together during the war.”

^{Helen McCrory with husband Damian Lewis (REX)}

As Aunt Poll, McCrory exudes a sense of loss and broken beauty that only an actress who still has full use of her facial muscles could pull off so convincingly. Although she jokes that she has now grown a fringe, to hide any encroaching lines, McCrory has always resisted the pressure to conform to Hollywood stereotypes.

She is regularly cast in big films, including the Harry Potter series, Skyfall and Martin Scorsese’s Hugo. But she also excels in dramas that place 40-something women at the centre of the story, including last year’s television series Leaving, in which she played a hotel manager who has an affair with a man 20 years her junior.

“Just a week ago I was offered a part where I was a bit concerned there was more sex than talking,” she says. “It’s great to still be offered that stuff. But whatever the part, I’ve always been more concerned about the story I’m telling and telling it accurately than how I look.

“When we filmed Charles II, I insisted on having thick white paste layered on to my face every morning that flaked off in horrible lumps. When I saw the edited film and all the other girls had American tans and lip gloss I thought: 'Oh my God, what do I look like?’ But that’s how I wanted to tell that story.”

^{Helen McCrory arriving for the Royal World Premeire of Skyfall at the Royal Albert Hall (PA)}

McCrory has never looked more glamorous than when she is alongside her actor husband, Damian Lewis, star of the hit American series Homeland. While other celebrity couples po-facedly shun the cameras, there is something rather refreshing in seeing McCrory and Lewis immaculately dressed up to the nines, her in vintage Givenchy, and him in white tie, literally having a ball en route to the Golden Globes, the Met Ball, dinner at the White House, the Baftas.

“We’re extraordinarily lucky that we’re having success at the same time,” says McCrory. “But also there’s nothing worse than someone on the red carpet saying: 'I hate this.’ Get a grip. Someone is sending beautiful Armani gowns to your house for you to wear and someone else is lending you diamonds for the evening. Of course it’s fun.

“We also know this too will pass. Enjoy it while you can. And we do have perspective – we have great fun walking the neighbour’s dog.”

At some point, McCrory suggests, the couple will certainly work together, although so far the parts they have been offered have been “too dark”. They were recently approached to do Who’s Afraid of Virginia Woolf?, Edward Albee’s searing play about an explosive marriage that was turned into an Oscar-winning film with Elizabeth Taylor and Richard Burton. “But, as Damian said, 'Oh God, not at ------- work as well,’’ jokes McCrory. “We’d be much more interested in doing comedy.”

^{Helen McCrory with husband Damian Lewis (REX)}

The couple also have two children, Manon, six, and Gulliver, five, who are barely aware of their parents’ careers. They live a relatively low-key family life in Tufnell Park, north London, and McCrory suggests her daughter would be “much more excited if I was a vet”. She does, however, acknowledge the impact that having children has had on her own work.

“It peels you of a layer of defence,” she says. “It’s like being naked. The slightest breeze and you feel it. I used to come to emotional scenes having rehearsed them all the night before. Now I barely look at them, because it’s all just beneath the surface and I want that full impact.”

Yet McCrory still has a reputation for the most detailed preparation. As our interview draws to a close, I ask her about her accent for Peaky Blinders, a century-old Birmingham dialect.

“I started learning mine from Julie Walters,” she says. “But they said it was too modern. So then I moved on to Ozzy Osbourne. Lord knows what that poor man has put in his body, but apparently he speaks a more old-fashioned Brummie. In the end the voice coach decided it for all of us. It has to be right for the time. So, as any 102-year-old woman from Birmingham will be able to tell you, I’m now absolutely spot on.”

'Peaky Blinders’ airs at 9pm on BBC Two on September 12