It's a rainy morning on the outskirts of Paris, the sky as grey as the puddles of mud churned up outside a nondescript warehouse; but, inside, something magical is happening. Walk along several dark and grimy corridors, and suddenly you see a room inside a room -- like a Chinese box or a conjuring trick -- where light streams out of the windows into the cavernous gloom. Navigate a path through the cameramen and film crew, and you find yourself within the inner sanctum of Coco Chanel.

Or at least that's what it looks like on the set of Anne Fontaine's film, Coco Avant Chanel, where an eerily accurate version of the designer's famous couture salon has been recreated down to the last detail, with a vase of white peonies on the glass-topped table, and the gleam of crystal chandeliers reflected in the mirrored walls. An etiolated model glides across the room, wearing a silvery-grey ankle-length gown; another stalks past in an exquisite pale gold sequinned dress; and more costumes hang from a gilt clothes rail, swathed in white silk shrouds, like gossamer ghosts. And then you see her, Audrey Tautou, the star of the film; a tiny gamine, eyes as dark as her black bobbed hair, mouth slightly down-turned in a moue of disapproval, scissors in one hand, a cigarette in the other.

"Astonishing," says a curator from the Chanel archive, who is working on the set today -- part guardian to the precious vintage pieces that have been borrowed for the filming, and part adviser on period detail. "It's like seeing Mademoiselle Chanel in the flesh." The curator shakes her head, very slightly, then turns her attention to a tray of pearls, rearranging them in precise circles.

Tautou is wearing a navy-blue silk sweater, a knee-length cream tweed skirt, and beige and black two-tone Chanel slingbacks; an outfit straight out of the early Fifties, though the models' gowns are from the Twenties, and Chanel's assistants are in long skirts and sober jackets that pre-date the First World War. Time slides and elides on the set -- the same scene is shot over and over, of Chanel snipping at a diaphanous pink chiffon frock -- and, as more models glide in and out of shot, their fingers occasionally brush at their diamond bracelets and pearl earrings, as if they cannot quite believe the reflections that they see of themselves in the mirrors.

The jewellery looks real, but it could be fake -- or both, in a combination made famous by Coco Chanel, who mixed precious stones and glass copies with a confidence similar to the way in which she blurred truth and lies.

All of which is entirely appropriate to the spirit of Coco Chanel, a woman with a life so mysterious -- and lengthy, spanning more than eight decades from her birth in 1883 to her death in 1971 -- that it would be impossible to reveal its secrets in a dozen films. Hence the fact that there is ample material for more than one forthcoming biopic: Audrey Tautou will be followed by another version with Anna Mouglalis, in a film that examines the designer's relationship with Igor Stravinsky, due to be released at the end of the year. (There have also been rumours of a Hollywood film in development, starring Demi Moore.) Both Mouglalis and Tautou are already known as faces of Chanel: Tautou stars in the latest No 5 campaign, shot by Jean-Pierre Jeunet, the director who made her internationally famous in Amelie; Mouglalis in the Chanel Allure perfume advertisements.

Tautou is well aware that there were many faces of Coco Chanel, even within the designer's own lifetime. "She was such a complex character, and full of contradictions," says Tautou, when we meet after the filming. "And she told so many lies about her past -- huge, enormous lies -- so that you can only understand her life little by little."

Coco Avant Chanel concentrates on the designer before she was famous, and it helps that Tautou looks uncannily like the young Chanel -- who was born Gabrielle before she reinvented herself as Coco -- and that she was also brought up in the Auvergne, a remote region of south-central France.

"It's in the heart of the country, far from the sea, and very isolated," says Tautou. "And so we have that in common, because there's something about the Auvergnat people -- they are very hard-working and strong-minded."

You can see why Fontaine wanted Tautou for the role: "The actress had to combine a slender silhouette with a strong temper, an iron hand in a velvet glove. Audrey has the slimmest waist in the world, though she also has this 'little black bull' side to her, as her friend the writer Paul Morand used to say of Chanel -- a grace, finesse and irrefutable charisma."

But the film explores Chanel's early life, when she was at her most defenceless, growing up in a convent orphanage, and her uncertain start in adulthood, working as a seamstress by day and a cabaret singer at night, before becoming the kept woman of a rich man who treated her, at times, with rather less respect than he did his racehorses. "She was a little girl from an orphanage in the middle of nowhere," says Tautou, "and she had to learn to pretend to be strong, to hide her vulnerability behind a facade."

Fontaine does not claim to be entirely historically accurate -- the timescale is intentionally blurred, as are Chanel's family relationships -- nor does the costume designer, Catherine Leterrier. "Period movies are sometimes too careful," says Leterrier, "but we didn't want to be conservative -- we felt the costumes could be as free as Chanel was." And, somehow, it works, without looking anachronistic; for example, the iconic navy and white striped sailor tops worn by Chanel in the Thirties are transposed to an earlier era to suggest her movement away from the convention of corsets and frocks. Similarly, Leterrier came up with an imaginative suggestion as to the origin of the legendary Chanel bag: "I drew a quilted sewing bag in the shape of the handbag, and had it made out of an old black flecked cotton canvas that peasants' clothing used to be made of, as if the young Coco had made it out of a remnant given to her by her aunts."

As it happens, Coco's "aunts" -- severe, black-clad women to whom she referred as her "guardians" following the death of her mother -- were in reality the nuns who ran the orphanage where she was abandoned, along with her two sisters, by her itinerant father. But Chanel never referred to the orphanage, nor to the austere circumstances in which she was raised, preferring, says Tautou, "to keep her sufferings to herself".

Fontaine quotes one of Chanel's own aphorisms -- "I invented my life because I didn't like my life" -- to give context to her reshaping of the past; but the film allows the audience to warm to a woman more often depicted as a cold-hearted careerist. We see her suffer a series of losses -- of her father who leaves her at the orphanage; of her dignity, when she sings in front of boorish army officers; of her virginity, in her early days as a demi-mondaine; and of her great love, Boy Capel, an English industrialist and playboy who Chanel lost twice over (first when he married another woman; and when he died in a car crash).

As Tautou herself observes, what emerges is a story about a remarkable woman who happened to become a fashion designer, but might equally have found fame as an actress or singer in her pursuit of independence. "I've always loved Chanel's style," she says, "but I was more interested in her character than the fashion. And I wanted to discover what lay behind the facade." To do so, Tautou read various differing accounts of Chanel's history and watched footage of her television interviews, but conceded it was impossible to be certain of the facts. "She became very professional, and life hardened her -- and the only thing that diminished in her was her doubts. But still, I felt it was important to show something of her vulnerability, because she always said that the one thing that accompanied her through life was loneliness and solitude."

It's an intriguing portrait by a beguiling actress -- and one who guards her privacy with even more ferocity than Chanel -- but perhaps the last word should go to Coco herself, who would doubtless have been amused by the multiplying versions of herself. "The legend has a harder life than the subject," she observed to Morand, when both were living in exile in Switzerland soon after the Second World War. "Reality is sad, and that handsome parasite that is the imagination will always be preferred to it. May my legend gain ground; I wish it a long and happy life."

Coco Avant Chanel opens on July 31. Coco Chanel, by Justine Picardie, will be published by HarperCollins in October

© Telegraph

- Justine Picardie