Helen McCrory is considering a career change. The acclaimed actress, widely considered the best in Britain, and the natural heir to Dame Judi Dench, says she feels more like a London cabbie doing the nightshift these days.

Just finishing her high profile role as Rebecca West in Rosmersholm at London's Almeida theatre, her life, she says, involves flitting from one role to the next - actress, wife, mother - and almost always at night.

"I've been acting in the evenings, then I'm home for the night feeds with Gulliver (her eight-month son), then up with Manon at six (her 22-month daughter), and having snoozes in the afternoon. It's like being a nightshift worker, a cab driver in London," laughs the 39-year-old.

Of course, if she really was considering such a career change, there'd be the small issue of getting her driving licence first - something she's never felt she needed, considering 'you pay as much for driving and parking in London as you do on black cabs'.

But, more importantly, she'd leave a huge, gaping hole in British TV and theatre talent, not to mention film, where her quirky, interesting roles almost always seem to have been written for her. Roles like Peggy in Flashbacks of a Fool with Daniel Craig, who personally requested her for the part, and Cherie Blair in The Queen .

"There are plenty of big films that are just not to my taste. Like the films that everybody knows are an absolute copy of another, filmed just because they know it will be money and bums on seats"

What's perhaps more likely, is that Britain will lose McCrory to Tinseltown. She's currently packing up Gulliver and Manon and spending her second consecutive summer in LA with her husband, the Golden Globe-nominated actor Damien Lewis, who's there filming the second series of the hit NBC show, Life.

Both classically trained actors, Helen is the daughter of a Scottish diplomat who grew up in Cameroon, Tanzania, France and Scandinavia, before going to boarding school in the UK and studying at London's Drama Centre. They met on the set of Five Gold Rings at the Almeida in 2004 and married in 2007.

A devoted couple, perhaps even the highbrow British alterative to Brad and Angelina, Lewis followed McCrory to South Africa when she filmed Flashbacks of a Fool, and she returned the favour in LA last summer while pregnant with Gulliver and looking after Manon. "Growing up as a family is important to us," she says, which is why she's back in LA again, supporting Lewis, but also auditioning for roles herself this year.

Judged solely on LA standards, Helen wouldn't have much luck. In la la land, actors, she insists, are judged by their paycheque. And her salary for Rosmersholm wouldn't get her too far. Yet she also has an enviable 18-year-career of mixed and mostly demanding roles in high profile films – Charlotte Gray , The Count of Monte Cristo , Casanova , and Interview with a Vampire – which put her firmly in the game.

Not that she'd be interested in the 'paycheque' movies anyway. "There are plenty of big films that are just not to my taste. Like the films that everybody knows are an absolute copy of one that's been done before because they know it will be money and bums on seats. I'm attracted to projects that are ambitious and ambitious for more than just making money."

Since becoming a mother, another driving force has also crept in when she chooses roles, and that's that they connect with her life in some way. She chose a modern version of Frankenstein for ITV when pregnant for the first time. "I sympathised because, let's face it, when you are pregnant, you never fully know that your child will be okay," she said then.

With Ibsen's Rosmersholm, she wanted to do some real life acting after returning from the 'emotionally suppressed' LA, and was won over by the director Anthony Page. "I really wanted to walk on stage and not have to 'act', and the play was interesting and true to life in that way."

"Helena Bonham Carter with mad hair and rolling eyes, Alan Rickman as the super-relaxed Snape and Jim Broadbent lurching towards you… the Harry Potter set was surreal!"

Helen's next project is another such choice. She plays Narcissa Malfoy in the upcoming Harry Potter film, The Half-Blood Prince, out in November. Originally cast as Bellatrix LeStrange in the previous film, Helena Bonham Carter took the role when pregnancy and flying stunts ruled Helen out.

But Narcissa is a much better fit. She's the sister of Bellatrix, the wife of Lucius, and the devoted mother of Draco, whom she's willing to sacrifice everything for – something McCrory can now identify with.

Doing Harry Potter was a treat in so many ways, she says. First, it's a big budget film in a British industry that's hampered by lack of finances. Creatively, Warner Brothers have left the artistic licence to the British team of David Hayman and David Barren, something that's highly unusual in the US movie industry. And then there's the number of high profile British actors all working together in one film - almost unheard of.

"There's Helena in Doc Martins, mad hair and rolling eyes, Alan Rickman as Snape who, if he was more relaxed, his heart would stop. Then Jim Broadbent is lurching towards you opening the door. It's surreal. These are actors normally playing lead roles and some have four lines here. So it's amazing creativity both on the acting and production fronts. There's this freedom to create which is quite unusual for Britain," she admits.

Narcissa is a role that will bring Helen back in the next two Harry Potter movies, along with further acclaim, no doubt. In fact, with this and more big projects on the way, perhaps 'paycheque' status isn't far off. It's certainly not for her husband, judging by the recent success of Life.

But they don't get caught up in all that. While McCrory did the nightshifts recently, Lewis spent his days doing up their Tufnell Park home, climbing ladders and knocking down walls, so much so that Manon thought it was his day job.

It's not quite the existence you might imagine alongside the Tom and Katie's, and Demi and Ashton's in LA. And that's the best bit. Having achieved creative and commercial success in their own way, let's hope this London cabbie and builder continue to stick to their roots.

By Barbara Walshe