Belle de toujours: A rare audience with fashion legend Inès de la Fressange

Intelligent. Mischievous. Absurdly glamorous. Carola Long meets the eternally beautiful icon of French style

Inès de la Fressange is running late, but its hard to hold it against her. Firstly, because I'm waiting in the twinkly warmth of an afternoon tea party at Roger Vivier's Sloane Street boutique; and secondly, because the reason she's been waylaid is so very understandable. She's been in Topshop. After stepping off the Eurostar, the former Chanel muse and model – and now the brand ambassador for luxury shoe label Roger Vivier– just couldn't resist a little detour to one of our national treasures. "I bought a sequinned jacket a bit like this one," she says, in her warm, deep voice, while gesturing with slim, elegant fingers at the sparkly black blazer she's wearing. It's part of an outfit that looks more quintessentially Parisian than an onion-seller eating a croissant under the Eiffel Tower. Her long, slim legs (she once likened her figure to a "giant asparagus") are encased in straight dark jeans, and teamed with a Breton top and midnight-blue velvet Vivier flats. At 52, she is strikingly beautiful with olive skin that's smooth, but not suspiciously so, and sparkly, dark chocolate-coloured eyes enhanced with smoky make-up. However, it's her manner that's most engaging: a combination of rapid banter, the odd sultrily-slurred phrase, animated gestures and conspiratorially raised eyebrows.

Whenever Fressange, who lives on Paris's Left Bank, comes to London she is "totally forced" to come to Topshop by her children, 15-year-old Nine, and 10-year-old Violette, but she also believes that, "it's really important to see what the street fashion is. In the luxury business if you see that something is sold very cheaply there is no point in trying to do the same kind of thing."

This kind of research and observation is part of Fressange's role at Roger Vivier. She explains that when Diego Della Valle, the chairman and CEO of the luxury leather group Tod's, hired her in 2002, after buying the Roger Vivier label, it was to take care of "the communication, the strategy, the decoration and all that". It was part of a plan which has successfully taken a label that had fallen from favour into a desirable modern brand, with six international shops, an opulent couture collection of shoes and bags, and famous customers such as Nicole Kidman and Cate Blanchett. One of Fressange's first projects was to choose the location for the Paris boutique and its interior design, and after taking advice from of one of the late Vivier's friends, she duly crammed it with an eclectic mix of art and antiques. "We wanted an elegant shop for elegant customers," Fressange explains, "to go back to what is real luxury."

The label's credentials certainly made it ripe for a revival. Vivier was credited with inventing the stiletto in 1954, and provided glamorous footwear for the likes of Marlene Dietrich, Brigitte Bardot, Liz Taylor and Françoise Hardy. He created heels with a fleur-de-lis motif for Queen Elizabeth II's coronation (the flats Fressange is wearing today are a homage to them) and Catherine Deneuve wore the designer's buckled pumps in the film Belle de Jour. They were designed in 1965 for Yves St Laurent's Mondrian collection, and the square, chrome buckle has been reinterpreted as the label's signature motif by designer Bruno Frisoni.

Just as Roger Vivier has a distinguished history, Fressange's own stellar status made her a smart choice to lend the brand some modern sophistication, coupled with the fact that she knew the late designer. Her background is absurdly glamorous. She is the daughter of an Argentinian heiress and a stockbroker with his own plane, while her couture-clad grandmother drove a gold Rolls-Royce. After becoming a model, her big break was meeting Karl Lagerfeld at the New York shows in the early Eighties, when he offered her an exclusive contract to be the face of Chanel. With her coquettish but confident air, Fressange became Lagerfeld's muse and he said he wouldn't design a collection without her. The fairytale came to an abrupt end seven years later, however, when the pair fell out, although they are now back on cordial terms. The row was supposedly because Fressange was asked to be the face of Marianne, the symbol of the French Republic – after which Lagerfeld labelled her provincial, castigated her in an interview, and Fressange's contract was ended. More recently she has said that Lagerfeld was probably put out because she had fallen in love with the man who later became her husband, art historian Luigi d'Urso, who died suddenly of a heart attack in 2006.

After her Chanel days, Fressange designed her own label for almost a decade, and was awarded the Légion d'Honneur in 2008. In October, she received another accolade, this time voted for by the readers of Le Figaro, who crowned her the most chic woman in France in their annual poll. She beat Carla Bruni – whom Fressange has known "since she was in nappies" – into fifth place. "They don't see me every day. I promise I didn't pay for it," is her laughing response. She adds, "I was very proud, of course, but my daughters were all giggling because they think of me in front of a pile of dishes screaming that I have nothing to wear. My daughter Nine did an interview for Teen Vogue in which she said that I spend hours in front of the wardrobe every morning, which is totally untrue because I have to take my little daughter to school at 8.30am!"

What does Fressange think distinguishes French style? "In England people follow fashion much more than in France," she says. "I imagine Bridget Jones working in an office and dying to go and buy a pair of shoes at lunchtime, you know. French women have a kind of arrogance. It's: 'I ignore fashion, I do my own thing.'"

In France there is also less of an obsession with youth. Fressange caused something of a sensation in January last year when she modelled for Jean Paul Gaultier's couture show. There was nothing tokenistic about her sultry turn and the audience were thrilled. "People were happy to see that Gaultier likes old ladies too," she jokes. "There he was showing that he likes all kinds of women. I think people were clapping for that too, to show that it's possible to be fine at 51, as I was then, without botox." She's also frustrated by the fact that it's "impossible to find a woman who is more than 30 years old in magazines. It's like being older is hidden, there's no one for women to identify with."

The secret of Fressange's longevity as a style icon isn't just her gamine bone structure and sinewy grace (she manages to make eating an overstuffed club sandwich while we chat look surprisingly elegant) but also her intelligence and mischievous animation. She once greeted Anna Wintour for a private viewing at Chanel by going into the changing room and putting on the same red suit and a pair of dark glasses and mimicking her. It's a testament to Fressange's charm that Wintour laughed. In the Eighties she became famous for subverting the catwalk's traditional poses and generally appearing to have fun – although she says that the highlight of her modelling career was "when I stopped. It's boring to be a model." Despite this, she rips through a list of catwalk memories with all the excitement of a child unwrapping a Christmas present. There was the time she took a bit of burnt cork and drew herself a huge moustache; the catwalk appearances with skis or her dog; and the occasion a photographer put a joke-shop knife on his head to elicit a scream.

It was also in the Eighties that Fressange pioneered the idea of wearing a Chanel jacket with Levi 501s, and as she wanders around the plush Roger Vivier boutique greeting customers with two kisses, she still looks the epitome of chic understatement. Although she sometimes wears heels, she prefers the fuss-free practicality of flat shoes, and is scornful of the way that "some people think that shoes are ladders. No man is going to say, 'I would love you so much more if you were 10cm taller'. Women are suffering, you know. Elegance is about feeling nice, how can you feel nice when you have shoes that are like a prosthesis?"

She particularly loves Vivier's flat "Chips"-style shoes, because "I can wear them during the evening or day, with a dress or with trousers. They can be classic and chic but never bourgeois or boring." The same could be said of the chic-est woman in France.