What does 1920s Birmingham gangster drama Peaky Blinders and an American western have in common?

More than you might think, according to Tufnell Park actress Helen McCrory, who’s back on our screens as the hard-as-nails Aunt Polly in the third series of the hit BBC show.

“Something that the Americans have understood is that they have mythologised their people.

“A bunch of cow herders going across the west are turned by John Wayne into a western. The gangster by [Martin] Scorsese has been turned into the hero.

“We don’t do it in Britain. We’re very, very good at self-effacing, detailed, beautiful, poignant, slate grey films, but we’re not good at mythologising.

“But [Peaky Blinders writer] Steve Knight has done it; and done it in Birmingham, about a bunch of people that no-one makes drama about.”

The drama’s increasing appeal to viewers, she says, is indebted to Knight’s writing and the quality of the production, pointing out that the last scene in the third series was shot entirely in one take.

The criminal gang underworld of Peaky Blinders may be far removed from McCrory’s off-screen life, but there are still some similarities between the actress and matriarch Aunt Polly.

They are the backbones of their families, and work incredibly hard: Aunt Polly, to keep her family together, and McCrory to keep up with her busy schedule.

“I never sit still,” says the 47-year-old mother-of-two. “I’ve got my own world and my husband’s world, and a house that needs cleaning, and washing that needs doing, and the kids – but I enjoy that full life.”

McCrory, who lives with her husband, Wolf Hall actor Damian Lewis, in Tufnell Park, speaks to me with a cigarette in her hand on the roof of the National Theatre, taking time out of her hectic rehearsal schedule for upcoming play, Deep Blue Sea.

The revival of Terrence Rattigan’s 1950s piece – about a woman, Lady Hester Collyer, who has just attempted suicide after cheating on her husband – sees McCrory reunite with director Carrie Cracknell after playing the title character in the National’s production of Medea in 2014.

It promises to be different from any Rattigan production ever staged before.

“People will say, ‘oh I love Terrence Rattigan’ and immediately think of an ebony cigarette holder, a pencil skirt, and smelling of Yves Saint Laurent – but he’s a brilliant playwright.

“I imagine he must be so frustrated if he was alive today to think that everybody treats his stuff like a history play. Whereas with Shakespeare, I don’t think I’ve seen a Richard III that isn’t set in Nazi Germany.”

She adds cautiously: “If it works. I’m terrified because I’m sticking my neck out, but you’ve got to try these things.”

But we’re talking because she is patron of the Sir Hubert von Herkomer Arts Foundation, a Camden-based charity which gives a top-class arts education to children from north and east London schools who might not otherwise have the opportunity.

Last Thursday, she attended a gala with husband Lewis at University College School in Hampstead to launch the charity’s new programme of poetry classes, which will be taught by professionals at the school.

“It’s not just about creating the next Chapman Brothers or the next Ian Rankin; it’s also about preparing children to express themselves freely.

“We have problems with knife crime because we’re in a world where children are frustrated and feel unable to express what they feel other than through brutality.”

It was her Foreign Office diplomat father who taught her to draw rather than her Royal Free physiotherapist mother, and now she teaches her own two children, aged nine and eight.

“Kids now are being shown really sophisticated images and thoughts, but actually having to work with their hands – I don’t think you can underestimate how calming that is. I find it calming for me too.

“As a mother, sharing art with my children showed me how beneficial art is to all of us.”

With both parents actors, it would be all too easy for the family to be sucked into the glamorous showbusiness lifestyle.

But McCrory says their life is more play dates on Sundays and bike rides in the park than red carpet events and celebrity parties. She had to make one exception, though, when the invitation to the premiere of the new Star Wars sequel, The Force Awakens, came through the door.

“It would have been too cruel not to take them,” she laughs.

“It was great fun but they kept asking: ‘Mummy, when’s it starting?’ So I think next time, we’ll just go back to the Holloway Odeon.”

But before then, there’s plenty more projects in the pipeline for McCrory.

Her next two films are both in post-production: Their Finest Hour and a Half, a romantic comedy starring Gemma Arterton and Bill Nighy, and Loving Vincent, about the life of Vincent Van Gogh.

It will be the first feature film to be animated using oil paintings, and each frame has been painted by hand.

McCrory says she uses only two criterion for choosing a role: excellent writing, and having a good director attached to the project.

“Great writers find narrative in life and we all look for narrative in life.

“When working with great writers, you’re privileged enough to express the most complex thoughts with beautiful language.

“After all, actors are just a bunch of people who aren’t good at writing their own words.”

More information about the von Herkomer foundation. To ask about donating, email donate@vonherkomerfoundation.org.