Helen McCrory: The dame game

She's a West End star who's about to join her husband in Hollywood. No wonder critics call Helen McCrory the next Judi Dench, says Hannah Duguid

Despite being one of Britain's foremost actresses, Helen McCrory is rarely recognised in public. Recently, a taxi driver refused to believe who she was. "You're not Helen McCrory," he said. She was unable to convince him of the truth. I can see how he made the mistake. In the flesh, despite having given birth only a few weeks before, she is slight, pretty and, although a formidable presence, does not remotely resemble Cherie Blair, whom she portrayed so convincingly in Stephen Frears's film The Queen. "I've often sat down with people talking about a film I've been in and they haven't realised I was in it. I think they're just being weird by not saying anything until I realise what has happened," she says. Not that she is phased by any of this: "What really matters to me is what my peers think."

Her marriage to the actor Damian Lewis the couple have two children has occasionally propelled her on to the pages of magazines. But McCrory and Lewis seem as well grounded as it is possible to be when you're one half of a famous couple who divide their time between north London and Los Angeles. There are flourishes of luvviness "darlings" and enthusiastic swearing with a cut-glass accent yet they are clearly devoted to each other. He accompanies her to our meeting at a Soho restaurant and settles her and their tiny baby son into a corner table before politely disappearing.

McCrory is now 39 and her acting credentials are impeccable. Often compared to Judi Dench, she has appeared in more than 40 plays, winning prestigious theatre awards for her performances as Elena in Chekhov's Uncle Vanya at the Donmar Warehouse and Rosalind in As You Like It although her talent in that production was somewhat overshadowed by co-star Sienna Miller's celebrity. "I love theatre because it's just me and the audience," she says. "It's the litmus test in acting, to be able to sustain a performance over one, two or three hours."

As well as numerous television roles, she has played supporting characters in films such as Charlotte Gray, Enduring Love and Casanova. In March, she will appear in Flashbacks of a Fool, the feature debut of the British writer and director Baillie Walsh; the lead character is being played by Daniel Craig. Walsh is best known for directing music videos, yet Craig and McCrory immediately agreed to appear in his first film. Craig's enthusiasm was such that he helped raise funds for the project.

"It was a very good script," says McCrory now. "And the way Baillie spoke about it was inspiring. If I meet a director and it's good script but they don't know their arse from their elbow then I don't do it. A script is only as good as the director who's making it. Baillie is the most thorough director I have ever worked with. The film is funny and it's sharp; it reminds me far more of modern American stuff. It's not cruel but it's black humour."

The story follows the life of a washed-up British actor in Los Angeles, played by Craig. With his career failing, he resorts to a life of cocaine and sex with prostitutes. He receives a phone call from his mother about the death of a childhood friend and returns home for the funeral. The film is an exploration of the past and of childhood memory. "This is what attracted me to the script," says McCrory. "Baillie has the ability to write about the past in a very transient way; our past is as transient as our present or our future. There's no such thing as a definitive past, and this is what Baillie is looking at."

McCrory's next project will be another British venture. She will appear as Narcissa Malfoy, wife of Lucius Malfoy, in Harry Potter and the Half-Blood Prince, the sixth film in the series. Filming is about to start. "I'm looking forward to it. It's unusual to have such a successful film only starring British actors. I have really started to enjoy the craft of film acting. I do a lot more film and television now than theatre. The difference between screen and stage is that in theatre it's tangible whether someone can act or not. I've worked with people, who will remain nameless, where a film scene has had to be cobbled together from a whole day's worth of takes because the actor is shit. They can't remember the lines; if they do remember the lines, they can't remember the moves. In the final project, they will look great, because the director will cut the film for them. In theatre, you can't employ someone who can't remember their bloody lines. That's the difference," she says.

During her childhood, McCrory lived in Cameroon, Tanzania, France and Scandinavia. Her father was a Scottish diplomat, and she did not settle in England until she was sent to a girl's boarding school. It is this expat lifestyle that she attributes to her late entry to film acting. "I used to be really ignorant about film. I didn't know anything about film culture or film actors and I still haven't seen many of the great movies. Damian's a great film buff and he really introduced me to them. I suppose a part of me thought my ignorance was slightly charming, but actually it's my job and I should bloody know them. We watch a lot of stuff now. The more I see, the more I appreciate it, and the more I'm excited about being involved in it."

So we will be seeing more of McCrory on the big screen, although with her highbrow standing, it is unlikely she will sell out to big-bucks Hollywood trash. "I'm not into mainstream Hollywood. Not because I'm a snob, it's just because I don't like it; it's not my thing. I'm not really their demographic anyway. I mean, I just get in rages about things, so I think it's easier for me not to watch it all those big tits and guns."

'Flashbacks of a Fool' opens on 14 March; 'Harry Potter and the Half-Blood Prince' opens in November