Helen McCrory: 'I used to think sexually charged roles were exploitative. Now I'm in my forties, I think it's art'

"I seem to be incredibly low," Helen McCrory complains, swivelling in her modish chair. In the arch-tones of a tabloid journalist, she declares: "Helen McCrory seems to have shrunk enormously since I last saw her. So it was no surprise when she told me she was starring in The Hobbit. I knew she was Welsh, but really?"

At a private members' club, wolfing down breakfast, McCrory, 5ft 3in, looks like an angelic child rather than a woman of 44 who just happens to be married to Britain's most desirable man – Damian Lewis, 42, the Emmy- and Golden Globe-winning star of Homeland. These days we see her on the red carpet, wearing slinky Marchesa frocks and De Beers diamonds. But McCrory seems enviably normal, with the actor's gift of intimacy and silliness. In that deep, thespy voice she can segue from Chekhov to contact lenses, and make both sound equally thrilling.

In the past two years she has played a Cabinet minister in Skyfall, terrified as Narcissa Malfoy in Harry Potter and the Deathly Hallows, and was hand-picked for Hugo, Martin Scorsese's Oscar-winning children's film. Oh, and she's just received an Olivier Best Supporting Actress nomination for her role as a fortysomething daughter at odds with her ageing hippie mother, played by Julie Walters, in The National's The Last of the Haussmans. It was a performance to make you howl and weep with recognition.

Getting the Bond job felt like serendipity, she says. She had worked with Daniel Craig on the movie Enduring Love, and was in the same restaurant as Craig when he heard he'd been cast as Bond. "We got rickshaws in Soho and went in search of drinks to celebrate. So it felt lovely to be going on to the set of a Bond film a few years later."

Last time we met she had two children under two and was clearly shattered, with dark bruises under her eyes. Today, she radiates energy. She says the children, son Gulliver, six, and daughter Manon, five, are now beyond the "Calpol" years. And she and Lewis are enjoying a moment.

Homeland has made Lewis one of the biggest British stars in the world. Last year, the couple found themselves at the White House at a state dinner thrown in honour of the British Prime Minister David Cameron. They had expected to be minor guests sitting somewhere near the kitchen. Instead, they found themselves at the top table with the Obamas. Both, it turns out, huge fans of Homeland.

Lewis's new status has given McCrory licence to pick and choose roles. And she's suddenly playing complex, sexually charged women. "At 21, I thought that kind of thing was exploitation. Now I'm in my forties, I think it's art."

In ITV's Leaving (written by Tony Marchant) she played a married mother in her forties who became sexually obsessed by a much younger colleague. Many of the scenes were shot in her underwear. It was Lewis himself who told her she was mad to keep turning down risqué scenes – and viewers responded. "It was amazing the number of letters I had from women saying, 'What a refreshing, wonderful thing to see,' and also, 'Why the hell didn't they get together at the end?'"

She hates the way society has double standards when a woman such as Sam Taylor-Wood has a younger partner. "People go on about me getting these Mrs Robinson parts. I keep saying to Damian, you're cast with a woman half your age, and nobody mentions it in the script. I only have to look at a younger man and the whole fucking drama is about it. 'My god, there's a woman with a job and she's looking at a man half her age,'" she hams like a preposterous old colonel. "'And he's looking back. Scandal, Daily Mail.'"

In her new film, Flying Blind, a political thriller by the Polish director Katarzyna Klimkiewicz, she plays Frankie, a brilliant aerospace engineer obsessed by her work.Frankie isn't short of male attention – she's just dumped a man who said "Thank you" and cried after sex. But when she meets 24-year-old Algerian student Kahil, her world is turned upside-down. Passionate encounters in dark alleys and slammed against the windows of her Georgian townhouse make her reckless. But is Kahil quite what he seems – especially given Frankie's work on government-sensitive projects?

Klimkiewicz is a first-time director, but what set the role apart for McCrory is that it isn't a silly Mills & Boon confection, where the woman is reduced to staring out of the window going: "What would Roger think or do?" It's the woman who drives the action. "You see it so much now on American television. So many of these big series are being launched with women in their prime as the leads."

Your forties are the most interesting part of your life, she argues. "There's so much complexity. And dramatists are recognising that now. Friends of mine are burying their parents or lamenting that they didn't have children or had too many children, worrying about the work-life balance. It's a key point in women's lives."

Anyway, older women are hot, she laughs. "They don't dress like people did in the 1950s, in age-appropriate cardigans. They have diets and the gym and great clothes. There's not that, 'My God, there's such a difference between a 20-year-old and a 40-year-old!'"

Plus, financial independence means the marriage contract has changed. "Women don't have to look for someone to pay the rent when they're looking for a lover." Which has freed men, too. "The benefits of feminism for someone like my husband are fantastic. He can stay at home with the kids, he can take them to a park, he does the school run. He gets to know his kids because that's expected of men now. No longer do fathers sit in the study and say: 'Bring the children up with my gin and tonic and I'll kiss them on the forehead.' As much as he may ask," she cackles suddenly, "he's not getting it."

But then, as she sighs, your forties are also a decade when you embrace the complexities of the modern world. "You suddenly find out where your coffee is being bought from and whether the company you're buying from pays tax on it. Your relationship with living in London, being responsible, becomes far more complex."

Ethical responsibility crops up a lot in McCrory's conversation. "I think I was brought up with an innate sense of responsibility because my dad was in the Foreign Office, where you were in somebody else's country, and you were aware of your behaviour. And my mum worked for the NHS, so you were aware of your responsibility to your country. I become such a socialist when it comes to the NHS. I'm really concerned about what's happening, and that people aren't standing up in the streets and demanding that it's better managed. It's ours."

McCrory had a peripatetic childhood – a good training for an actor. Her father was a Scottish diplomat and they lived in Cameroon, Tanzania, France and Scandinavia. Her mother was a physiotherapist at the Royal Free Hospital in London when her parents met, and she always worked; in Africa she set up a library, taught English, and travelled around Tanzania vaccinating children.

Her parents taught her that life was an adventure. She tries to do the same with Manon and Gulliver. "At the end of the day, I say: 'What did you learn today?' Then I have to say what I've learnt. I remember as a kid feeling indignant that I was the one under pressure, like a specimen."

In her teens, McCrory went to boarding school in the UK, then trained at the Drama Centre. Her first TV film, Karl Francis's Streetlife (1995) with Rhys Ifans, won her the Royal Television Society's Best Actress Award. "I had a bleach-blonde crew cut and my nose pierced."

Later came Anna Karenina and Joe Wright's Charles II: The Power & the Passion. She dated actors Rufus Sewell and James Murray, then met Lewis, when they played lovers in Five Gold Rings at London's Almeida in 2003 – but only got together a year later. "It was a slow-burn relationship." She had "no broody instincts, none, until I met Damian. It was his great genes talking." They married in 2007. They lived in LA for a year when Lewis filmed the US series Life – but she found it an "alien culture". The cult of confidence does nothing for her. "Self-doubt is very important. You should question yourself and ask how you can improve. I can't think of any situation where entitlement is attractive."

Now that she has children herself, she couldn't justify a role by saying, "Oh well, it's a big studio film and they're paying me loads of money" if the only women portrayed in the film were victims. "There are things I have turned down because I thought it would be irresponsible to make them – autobiographical women where you think: 'This is irresponsible if all you're going to do is talk about her affair with some prime minister when in fact she was an extraordinary woman in her own right; this just peddles the lie that women are only interesting in relation to the man they were sleeping with at the time.'"

Violence is another turn-off. She and Lewis were at the cinema at the weekend, watching the trailers, and "I turned to him and said: 'What is this depraved world that people live in?' There were girls slapping their arses and shooting off a bridge; in another one, a guy machine-gunned aliens in the head." It horrified her. "I think it's the responsibility of creative people to show people an option. Everyone can see how bloody awful the world is, but only a few people have the imagination or the intelligence to write about alternative ways of coping. To constantly reaffirm how terrible the world is just adds to people's loneliness and their sense of alienation from each other.

"Having said that," she brightens, "I've also played a woman in Doctor Who who's half-vampire, half-squid, so let's not get too heavy about it!"

You don't have to be in McCrory's company for long to understand why she has been cast twice as a formidable Cherie Blair (in Stephen Frears' The Queen and follow-up The Special Relationship). When Blair was asked who she'd like to play her in a film of her life, she replied: "Oh, Helen McCrory seems to be doing a good job."

McCrory and Lewis still take the Tube and live in a house in Tufnell Park, where the Holloway Odeon is their cinema of choice. They juggle the childcare. "As the Americans say, it's a high-class problem." But does she ever tire of her husband's new-found fame? "I tell you what, the mobile phone doesn't help. I've never seen Damian refuse an autograph, and he never would, because it's a nice thing. But mobile phones stuck in your face without permission can be very intrusive.

"We're particularly aware of it when we're with the children. Because we don't talk about our lives when we're with the children. They're five and six. They couldn't really give a toss about how much your film made over the weekend. Also, I think it's very important not to grow up with the unhealthy amount of attention that is sometimes put on people because they are 'actors'. If Daddy had suddenly discovered the cure for cancer, I'd understand more."

Lewis is now back home from filming Homeland in North Carolina (where he spends five months of the year), so McCrory can take time to film A Little Chaos with Alan Rickman and Kate Winslet, set in 17th-century Versailles. She's also just been filming a six-part television drama called Peaky Blinders, alongside Cillian Murphy and Sam Neill about a razor gang who operated in Birmingham.

"It's written by Steve Knight [Dirty Pretty Things, Eastern Promises]. As a little boy he was asked to deliver an envelope to a relation. He walked into this two-up, two-down and found this illegal betting shop with these beautifully dressed men surrounded by piles of money. The whole look of the drama is so original and fresh. It's a world you've never seen – the slums of Birmingham with 1920s gangsters. And it's filmed like a Western."

after our meeting, McCrory is off to raise money for Tommy's, the charity that funds medical research into miscarriage, still-birth and premature birth. At times, you sense that she finds the A-list life absurd. I tell her that at a recent film awards, every reporter was on the phone pleading, "But what is Helen McCrory wearing?"

"Now that's very nice," she laughs. "I love dressing up. But I'm very low-maintenance; the week before an event, I'll choose something as quickly as possible and that's that. If I can do my own hair and make-up, even better. I like it to be fun. It's very odd when you meet people a month before the occasion and they say, 'I'm going to wear so-and-so, what are you wearing?' and you think: 'I haven't any idea, love. That's in 28 days' time. I've got school pick-up.'"

She's proud of Damian's dress sense, though. "He wears a suit well; his father is quite dapper." Does she help choose his clothes? She roars with laughter. "Anything that looks interesting, I discovered, is only worn by the gay community. I think you understand the exchange that goes on there without me getting anyone into trouble." Menswear is so conservative, she sighs, though Tom Ford is "a genius".

She couldn't care less about "prettiness", meanwhile, and doesn't define herself by her looks. When people remark that her daughter Manon is pretty, she retorts. "Yes, she's very clever; she runs very fast."

Best of all, she seems fearless about ageing. Partly because she already knows what she's going to look like.In Scorsese's Hugo, she played both a 25-year-old actress and a rather chic 65-year-old grandmother. The director says that he chose her because she can portray so many different decades – with that urchin face and deep-set eyes.

"Actually, I'm looking forward to being 50," she teases, "because to me that's when a woman is at the pinnacle of her femininity and her womanhood."

'Flying Blind' (15) is released on Friday