As a mother of four, Meryl Streep knows all about wanting the best for your children. But, as she tells Steve Pratt, she's glad she's nothing like her character in her latest movie.

Meryl Streep puts her hand behind her head, pushes it down the back of her dress and pulls out a still-attached price tag. Only moments before, the Oscar-winning actress had said she believed that "what you wear announces something to people".

So what does failing to remove the tag from her outfit say about a woman described as Hollywood's greatest living actress? Just that she's on a busy publicity schedule for her latest film, The Manchurian Candidate, and has to leave the details, like what to wear, to other people.

Ironically, she has a reputation as someone greatly interested in costume. "In my next life I'm going to be a costume designer. But I'm incapable of dressing myself. Someone dressed me and they left the thing on. I've just realised that," she says.

This isn't what you expect from a Hollywood star with no less than 13 Academy Award nominations. But Streep in the flesh is a pleasant surprise. She comes with no movie star airs and graces that might be expected of an acclaimed actress who made her feature film debut as Jane Fonda's society friend in Julia nearly 30 years ago.

She's combined an impressive film career with a long marriage and raising four children, doing it without the self-publicity and fuss that many working movie mothers do. Family comes first, making a return to the theatre is unlikely in the immediate future.

"I love making movies because it allows me to be home at night. I have one child still young, 13, and like to be home at night and on weekends," she says.

If she can be difficult or a diva, she hides it well while promoting The Manchurian Candidate, a remake of the 1960s political thriller in which she plays a senator with presidential ambitions for her son.

She'd never seen the original, in which Angela Lansbury played the mother opposite Frank Sinatra and Laurence Harvey. "I'm not really a cinephile," says Streep. "I don't have an encyclopaedic knowledge of movies. So I missed it on the first go round. I would have been very young then anyway.

"When I got the job, I decided not to look at it, because I thought I might steal something from Angela Lansbury, and she wouldn't appreciate it. Or I would be affected by the performance in some way and maybe react to it or do something arbitrary, not to be like her."

She didn't have time to read Richard Condon's source novel either. "I was reading other things and watching a lot of political television. I was doing my homework that way," she adds.

"I have a busy life and not many people, who have a career that's time-consuming and have four kids, do go out a lot to the movies. I can barely keep up with the current crop to responsibly vote on behalf of the Academy Awards.

"It's like all the books you want to read. I try to keep current with the books I want to read this year, but I look at all the things I haven't covered in the classes. So there isn't enough time in life, that's all."

The political views of Eleanor Shaw, her character in The Manchurian Candidate, don't line up with her own. She sees her as "the full embodiment of everybody's fear of women in power". Everyone in England thinks it's Maggie Thatcher, while everyone in America thinks it's Hillary Clinton because they're the two most formidable women in political life.

"People have their fears, but those two women couldn't be more dissimiliar from each other or from this character that I play. We're touching on something very deep about Mommy and the fear of her taking over, or something," she says.

Getting the costume right was a necessity for clothes-conscious Streep, who calls herself "a pain in the ass" to every costume designer with whom she works because she has strong views on the subject, especially when she thinks of women viewers.

"When I sit with my husband in a movie, if the female character is bra-less, he notices. Other than that, it doesn't register. But we read the clues of our women characters so closely.

"It was very important for Eleanor to have good jewellery. We borrowed a lot of it and had lots of guards on the set - not for our well-being, for the jewellery. The clink of those heavy pearls was like the clink of power and entitlement, and all those things that being inside the beltway in Washington, and having that kind of access to power and money, conveys. I thought that was important, and the power suit is a trophy of that kind of woman."

A woman as successful as Streep is well placed to know the state of roles for older actresses. What she liked about The Manchurian Candidate was that a woman drove the plot and dynamics of the story so forcefully, aggressively and terrifyingly. Things are changing for older actresses with cable companies like HBO and Showtime making films for TV that reach a great many people. Some of the most exciting work now is happening there.

"There are many more independent pictures and they are giving opportunities to older women. In my case, the biggest reason that I'm working is that there are two women at the heads of studios where I've worked in the last few years," she says.

"Amy Pascal, who runs Sony Pictures, gave the okay for me to be in Adaptation. That was really a part written for a 35-year-old, but the director said he wanted me and she said fine. Another studio head would have said, 'Let's get somebody 16 years younger'.

"But I do think it's harder for the studio heads that are men to be interested in stories that resemble their first wives."

She'd never run for political office but makes no excuses for finding the humour in Eleanor. "Everything serious has something funny in it and everything funny has something tragic embedded in the bottom of it. That's the Chekhovian way of looking at things," she explains.

"That's the way I see life, so I couldn't play her as a straight ahead Gorgon. It didn't interest me because people that get things done in Washington have charm, often in big measure and they're pushy.

"And not just Washington, I think in the world. So it helps to round out this character with a sense you get of her own understanding of how monstrous she can be sometimes. Of her self-awareness."

She's not a pushy mother like Eleanor. "If you have children you're poised between hope and despair all the time, hoping for the best and worried that something is going to come out of the blue," she says.

"These are the things you can't control, but you do as much as you can. I have three that are now over 18 and one who's 13, and it hasn't eased up, the worry."

Having seen her in so many serious and downright tragic roles, Streep's sense of humour is a surprise. But then she does describe her work as fun. "It seems illicit how much fun it is," she adds.

"When other actors like you, that's really good. I really like it when young people, my children's friends, like my work. It's very gratifying to have that recognition."

At 55, she still hardly looks ready for old lady roles. She still looks good. "Bless you, but you're sitting far away," she says. "I remember what Catherine Deneuve always said, 'After a certain age you can have your face or you can have your ass, it's one or the other'. I've chosen my face, and I'll sit on the rest of it. My laurels, I mean."

* The Manchurian Candidate (15) opens in cinemas on Friday.