Meryl wears Prada

"The second time I watched the movie, I tried to imagine a man who was maybe 6ft 2in, nice-looking, greying hair, delivering the lines almost the same way she did and realised that there would be absolutely nothing offensive. Women are expected to wrap their request in a special package. On movies, male directors don't have to do that. Female directors do. It's the secret misogyny embedded in our society."

Streep says that she based the character on people she knew in fashion: the late Liz Tilberis (editor-in-chief of Harper's Bazaar), Polly Mellon (fashion editor at The New York Times) and Diana Vreeland, who ran both Harper's Bazaaar and Vogue before her death in 1989. They are women she admired, "very hardworking people in the world of fashion".

Rumours abounded during filming that costume designer Patricia Field struggled to persuade designers to lend her clothes because they feared incurring Wintour's wrath. More gossip followed about last month's charity premiere of the film. Wintour herself, who had kept a gracious silence when the book came out, was to attend, reportedly after a personal invitation from Streep and an assurance that Wintour had not been the basis of her characterisation. She could have cited the patrician East Coast American accent that she adopts for the film, rather than Wintour's unmistakable Queen's English.

"Someone did invite Anna to the premiere," Streep confirms while making it clear that she didn't issue the invite. "I don't know her and I had never met her. She sat a couple of seats in front of me and we were introduced and she was very, very cordial and it was fine."

Wintour's spokesman issued a statement the day after she saw the film: "She thought it was very entertaining. It was satire. What's not to like?"

The same day, the American industry bible Women's Wear Daily found plenty not to like, detailing in full the fashion faux pas in the film. Not only did it bemoan the "plain wrong" make-up, but asked: "Where are the insider clothes? Where are the hip labels that editors champion?" Even worse, it "played to outsider notions of how editors might dress".

As for the Priestly style, Patricia Field, who also created the looks of Sex and the City, dressed Streep in smart ensembles by Valentino, Oscar de la Renta and, of course, Prada, while Streep came up with the shocking-white hairstyle that is Miranda's signature in the film in the way that Wintour's highly sculpted, brunette bob has become hers.

"These women choose something that doesn't look like anybody else," Streep says. "They choose that look and stay with it through every fashion trend. I liked the vanity of it. The vanity of choosing not to colour your hair in an industry where everything would scream at you to be youthful and dye your hair. There's a special sort of vanity in having beautiful, naturally white hair."

Ironically, Streep, who turns 57 today, is completely uninterested in fashion. She might borrow from Valentino for premieres but she insists that she is happier in jeans and a T-shirt.

"I'm interested in clothes only in the choices my characters would make rather than the design. I mean, it's just the way I am. I know it's a multi-billion dollar industry, but so is aeronautical engineering and I am not interested in airplanes or being a jet pilot like John Travolta. I am just not interested."

Her indifference turns to anger, however, when she talks about the often damaging impact of fashion on the lives of young women. With husband Donald J Gummer, a sculptor, whom she married in 1978, she has a son, Harry (27) and three daughters: Mamie (aka Mary, 23), who has just made her off-Broadway stage debut in Mr Marmalade; Grace, 20, and Louisa, 15, who both still live at home.

"They all think there's something dreadfully wrong with how they look. Maybe that's a function of the human condition but I think it is reinforced by fashion magazines. I know how inadequate they made me feel, so I've always tried to tell them that it's what they do, not how they look that counts. That's hard in a culture which only values you for how you look."
Streep still looks as distinctive and beautiful as ever and is probably the hardest imaginable act to follow for her actress daughter - she's been nominated for a record-breaking 13 Oscars. Before the release of The Devil Wears Prada, she is already scoring a surprise hit with her all-singing role in Robert Altman's A Prairie Home Companion, as the mother of teen star Lindsay Lohan.

She says she feels "maternal" towards both Lohan and Hathaway. Indeed, The Devil Wears Prada is most interesting to her as a film about the choices young people make when assessing their goals in life. "I think it's about work, and about what part you're going to let work take over your life. They are things my own kids struggle with and they are good questions to ask."

Most, though, will find The Devil at its most delicious when offering some insight into the tough world of fashion. While some were allegedly too fearful to co-operate in the film, other fashion figures did take walk-on roles - supermodels Giselle Bundchen, Bridget Hall and Heidi Klum, Valentino playing himself - while designers such as Calvin Klein, Donna Karan, Hermès, Roberto Cavalli and Badgley Mischka lent their labels. It looks like being the must-have movie of the season.

The Devil Wears Prada opens in the UK on 27 October.