A Little Chaos: Helen McCrory talks teaming up with Harry Potter co-star Alan Rickman

"My dad's got a Glaswegian accent," she says, which is something of a surprise. She nods in agreement. "I sound like I come from Suffolk!" she adds, pronouncing it 'Suff-auk' - for emphasis - as if she were schooled at Eton.

She continues, keeping the oh-so-posh voice on for comedy effect. "People are like, 'Oh, hello, where do you come from?' And I say, 'I come from West Africa, actually!' But you can't tell."

Confused? Well, that's just what it's like meeting McCrory, a mistress of the deadpan, who is as entertaining off-screen as she is on. Her father is indeed from Glasgow, a former diplomat whose own father was a welder.

She did grow up in West Africa - Cameroon, to be precise - along with many other places, on account of her father's duties. And, yes, she does sound like she's from rural England. Put that down to time spent in a boarding school.

Such diversity has stood her well in a two-decade career that just seems to be growing in stature with every passing year. A titan on stage, this 46 year-old has twice been nominated for an Olivier award - for As You Like It and The Last Of The Haussmans.

On film, she's worked with Martin Scorsese (Hugo) and Sam Mendes (Skyfall). And on the small screen, she played Cherie Blair in The Special Relationship (reprising the role from Stephen Frears's movie The Queen).

The past 12 months have been particularly fruitful, with a Critic's Circle Theatre Award for her acclaimed performance as Euripides's eponymous heroine in the tragedy Medea.

She popped up in The Woman In Black sequel Angel Of Death, as a buttoned-down headmistress, and relished playing the villain with her Brummie matriarch Aunt Polly in the brilliant BBC 1920s gangland drama Peaky Blinders and her spiritualist Madame Kali in the Mendes-produced gothic serial Penny Dreadful.

It's not the first time we've met. Years earlier - longer than either of us would care to remember - McCrory and I spoke for Dad Savage, a thriller she made with Patrick Stewart.

She was a hoot then, as she is now. "I'm never going to be the actress," she told me then, "where they go, 'We need a body. Elle McPherson? No. Alright, Helen McCrory's available!' I'm never going to be that, so the parts I get offered tend to be interesting because they're not relying on the way I look."

Modest? Realistic? Perhaps both, although with these deep brown eyes of hers and dark lashes, there's something quite exotic about McCrory. If she once shut herself off from such parts, the last few years, at the encouragement of her actor-husband Damian Lewis, has seen her take on more sexualised roles.

In both Tony Marchant's ITV drama Leaving and the movie Flying Blind, she played women obsessed with male students 20 years her junior.

Her latest character has a frisson of eroticism about it too. The film is A Little Chaos, a sumptuous but sly period piece directed by actor Alan Rickman and set in the extravagant court of King Louis XIV.

Rickman plays the Sun King - naturally - and McCrory plays Madame Le Nôtre, wife to the visionary landscape architect Andre Le Nôtre (Matthias Schoenaerts), who was the principal designer of the elaborate gardens at the Palace of Versailles.

"It's a film about how gardens reflect the philosophy [of the time]," says McCrory. In other words, the highly ordered world of the French court, with the monarch at its centre, versus "the English philosophy" - man as a part of nature - as represented by the so-called 'little chaos' of the classic English garden, with its roses, brambles and wild flowers.

"Those two philosophies are brought really into a discussion about life," says McCrory. "How do you see life around you?"

Gardening metaphors may not sound like the most promising basis for a film, but Rickman's movie has a Dangerous Liaisons quality to it.

McCrory's hugely promiscuous Françoise, affronted that her husband should fall for his assistant (played by Kate Winslet), is a graduate of the "Dynasty school of bitchiness and wild revenge", as one critic put it. Watching her fume and scheme is one of the film's multiple pleasures.

McCrory has known Rickman for a while now. They were both in the Harry Potter franchise - he as Severus Snape, she as Narcissa Malfoy. "He's such an aesthete and you realise that by the way he dresses," she says.

"And as soon as you go to his flat, he has impeccable taste and that went into the filming." What was he like to be directed by? "He's very exacting," she winks. "But I loved working with him." She marvels for a second. "That delivery of Alan's..."

As luvvie as she can be, McCrory doesn't take herself too seriously. Not for one minute. We talk about Peaky Blinders. "I stayed away from Birmingham for quite a while after the first series came out, having heard my accent!" she chuckles.

"Also from my understanding that it was full of criminals that slashed each other!" Of course, it's hard to entirely relate - she and her husband entered a social whirlwind when he starred in the HBO hit Homeland, dining with Barack Obama at the White House.

She met Lewis when they played illicit lovers on stage in Five Gold Rings in 2003. They married in four years later, a wedding that came in the middle of an exhausting 14-month period where McCrory gave birth to their two children, daughter Manon, now 8, and son Gulliver, 7.

"I never daydreamed as a little girl of getting married and having children," she says. Work was always a priority, but when she got pregnant, they bought a family home in London's Tufnell Park.

She spent what she calls "the Calpol years" being there for her children 24/7, grateful that her career was robust enough to withstand a hiatus. Now it's all about juggling her and Lewis's blossoming workloads with the demands of childcare.

They have a live-in nanny, but they always want at least one parent to be there at all times. "It's got to be a damn good offer to coax me away from them," she says. McCrory's own "solid family" was clearly an influence.

Raised with a younger brother and sister, her early years were exotic by anyone's standards - Norway, Cameroon then Tanzania, all before she was 10.

"I loved it. You got to see, as a child, all these different cultures and realised there wasn't a wrong and a right. And that was fascinating. And if anything, it influenced me to want to be an actor. I enjoyed adapting to each different place I went to."

She has particularly strong memories of living in the beautiful coastal town of Dar es Salem, in Tanzania, spending hour upon hour every afternoon with her friends in the nearby Oyster Bay, with its thousands of sea urchins.

"In a strange way it was a very safe place to grow up because kids were on the streets, running around, and that's the African culture. Coming back here, I was quite amazed that children weren't allowed out and then, of course, as you grow older, you understand why."

When she returned to England, McCrory went to boarding school in Hertfordshire.

"That was interesting - just living with a lot of very rich children," she continues.

"It was like being in a different country." It was here, thanks to the inspirational acting teacher Thane Bettany (father to Paul), that she became enchanted by her craft. At 17, she applied for the Drama Centre in London, got rejected, came back a year later armed with a fistful of offers from other schools, and got in.

Theatre was always her first love. She didn't see her first film until she was nine, when her father sat her down to watch The Man Who Would Be King, while her life in Africa meant that television was a rather foreign pastime.

"I hardly ever watched TV. I remember the shock of watching the news - I'd be on the floor. People are getting killed!" Unsurprisingly, as soon as she graduated, she went straight to the stage, cast by Richard Eyre at the National in a production of Trelawny Of The Wells.

Winning McCrory the Ian Charleson Award - granted to the best classical theatre performance by an actor under 30 - McCrory never looked back. An early film role, as "2nd whore" in Interview With The Vampire, gave her a "fascinating" insight into Hollywood, where she was able to glimpse Tom Cruise and Brad Pitt up close.

"For the first time I realised what it was to be a Hollywood star," she says, but it wasn't for her. McCrory, for all her foreign adventures, has a real passion for homegrown fare.

With a third season of Peaky Blinders due in the autumn, she can next be seen playing Elizabeth I in Bill, a feature film comedy from the team behind Children's TV show Horrible Histories.

"They're like Monty Python for kids. They're brilliant. They're brilliant comics and actors. They've written about William Shakespeare coming to London to perform a play for the Queen, and he's a complete f***ing idiot!" She laughs with delight, a dirty Sid James cackle. Believe me, she no longer sounds like she's from Suffolk.

A Little Chaos opens in cinemas on Friday. Bill is released in August.