I prefer my boys to Clooney

Although it is a gloomy day, Natascha McElhone appears wearing a pair of huge sunglasses. She looks every part the glamorous actress: tall and elegant, lustrous blonde hair almost down to her waist, smart black polo-neck, trousers, and coat.

Then she takes the sunglasses off and apologises. "I wouldn't usually wear them unless the sun was out. It's just that I've got a black eye," she explains, smiling. "I was looking through a kaleidoscope with my son Theo on Friday and he accidentally bashed it into my face."

She orders a cappuccino and reaches for a shopping bag. "Look at this gorgeous thing," she says, pulling out a tiny striped cashmere jumper. "I bought it for Theo, who is three, but his brother Otis can wear it when he's older. He was only born in May, but I have to justify it somehow."

McElhone, 32, chats away as though we have been friends for years. It would be easy to forget that she is one of our most successful actresses, having worked with every A-list star from Robert De Niro and Anthony Hopkins to Brad Pitt and George Clooney.

Easy that is, except for the fact that she is so striking, with extraordinary eyes and a profile uncannily reminiscent of Meryl Streep.

She is remarkably down to earth and there is something ethereal about her too, an inherent calmness. She is, it seems, a surprisingly reluctant star who would rather discuss her children than show off about her co-stars.

Ask her about working with the elite of Hollywood and she shrugs, as though she couldn't possibly say it was her talent that secured such roles. "It is weird, isn't it? I don't really know how that panned out."

It has taken McElhone time to adjust to the media circus, a compulsory part of the job but one that she initially found strange because she was quite happy not being in the limelight.

"I remember going to premieres and always going in the side entrance of the cinema. It wasn't till much later that I made it up the red carpet. I wasn't being defiant, I just didn't get it."

McElhone has some impressive films to her name - notably Ronin, the 1998 thriller in which she co-starred with De Niro, and Solaris, which launched her into space with Clooney - but she wins these A-list roles without compromising.

It's not that she is casual about acting; it's more a case of having a young family, being grounded and not making a fuss about things.

She smiles. "I still want to work as much now that I have two young boys. Which is weird, because if I'm away from them for a day, my heart starts aching."

She says she loves America, where her older brother works, but only as a place to visit. "I just love coming home to London. I'm so urban. We live on a main street in Fulham but it never drives me mad."

McElhone has wanted to act for as long as she can remember. Her mother, the journalist Noreen Taylor, and her stepfather, former Daily Mirror editor Roy Greenslade - whom she calls "dad" - always encouraged her.

Her real father split with her mother when McElhone was two and she rarely sees him. She grew up in Brighton, but moved to the capital at the age of 15, and eventually won a place at the prestigious London Academy of Music and Dramatic Art.

Perhaps McElhone is so grounded because her parents have always worked in the public eye, but it is also due to the serious nature of her husband's job.

She talks with a great passion about Martin Kelly, a reconstructive surgeon who works at Chelsea & Westminster Hospital and cofounded a charity called Facing the World, which brings children from poor countries with cranio-facial deformities to London and "fixes them".

She is proud that he is capable of changing people's lives and does what she can to help; the proceeds from the premiere of Solaris went to Facing the World.

She certainly has a conscience - after her GCSEs, she went to Romania for a month to help orphans - but McElhone also simply wants to have a good time making films. She loved working with Clooney - "He's a laugh a minute, quite literally" - and talks highly of working with Christian Bale on the forthcoming Laurel Canyon, in which she plays an Israeli medical student living in Los Angeles who gets hopelessly caught up in a love triangle.

Although McElhone enjoyed working in America on the film, she would love to be directed by a British great such as Stephen Daldry, Sam Mendes or Stephen Frears. "And I'd love to do a play at the Almeida or the Donmar because it would keep me in London," she says.

She looks dreamy for a moment. "When you've taken time off to have a baby and you've become all nesty, you're desperate to get back out there - as long as it's not too far from home."

McElhone puts her sunglasses back on, gives me a firm handshake and strides off to find a taxi that will take her back to her family.