THE Cara Delevingne effect has hit Paris haute couture. It is fair to say that the women who wear Chanel’s bespoke fashion, where a made-to-measure jacket will set you back around GBP50,000, can emulate any wardrobe they choose.

This season, their icon is a trainer-wearing 21-year-old whose style signature is to make goofy cross-eyed faces in her selfies.

All 65 models on the Chanel couture catwalk — including Delevingne herself, who as muse and leading lady opened and closed the show — were wearing trainers. The boldness of this move by Karl Lagerfeld is such that, for the first time in years, the Chanel couture collection was not overshadowed by the theatrical sets that have become his hallmark.

Elaborate backdrops are an effective setter of mood, and the couture audience have found themselves in a futuristic jumbo jet one season, a bombed-out theatre another, each painstakingly constructed within the Grand Palais. But this season, all that was needed to conjure up a fresh vision of style was the trainers, which transformed the way the models carried themselves.

The collection was captioned “Cambon Club” after the Rue Cambon headquarters of Chanel and the set, all shiny silver surfaces and low, VIP-room sofas, was intended to evoke a nightclub. In fact, it looked more like a First Class lounge in a Middle Eastern airport, but no matter.

The revolving set took eight days to construct and will take four days to take down, apparently, but its central plot device was simple: a sweeping double staircase which afforded models full opportunity to show off their trainer-clad freedom.

It was a sight made all the more powerful by contrast with the effect stairs on a catwalk have when models are wearing, as they usually are, ill-fitting sample shoes with high, spiky heels.

Then, the anxiety and fear is clear as day on the young faces, two hours of makeup notwithstanding. In their Chanel trainers — each created in the ateliers of Massaro, makers of handmade shoes for the finest fashion houses in Paris — they radiated an infectious sense of ease.

The Chanel trainers came in blush-pink tweed, silver metallic thread, or pale lemon mesh.

In deference to the traditions of couture, the laces were transparent chiffon, but the soles — thick and spongey with the scrolled, supple contours made iconic by the original Air Max — placed them firmly in the tradition of sportswear and streetwear. At Chanel, where a flat shoe has traditionally meant a ballerina pump, and all the feminine delicacy that style implies, this was a major statement.

Chanel is not alone in embracing the flat shoe this couture season. Schiaparelli showed feathered pool sliders, while Dior’s ballgowns were teamed with crystal-embroidered mesh slip ons with boxfresh-white trainer soles. Even Carine Roitfeld, the French fashion editor whose front row style is revered in Paris, was spotted wearing flat boots to shows this week.

The casual mood is all the more surprising because the January haute couture shows are generally seen as a showcase from which actors can choose gowns for the upcoming red carpet season.

Could it be that Karl Lagerfeld, an astute reader of the zeitgeist, predicts that the more relaxed example being set by young stars such as Jennifer Lawrence — who livens up the red carpet with photobombing, and has repeatedly spoken out against the body-image tyranny of Hollywood — will create a desire for a high fashion with a less uptight attitude?

Certainly, the mood established by the trainers permeated the entire show. Even the full-length gowns were drop-waisted, flat-chested and feathered, evoking the spirit of those liberated party girls, the flappers. For day, the Chanel tweed skirt suit took on a whole new personality.

The jacket became T-shirt shaped, the sleeves chopped, the pockets and buttons — so prominent when Chanel is doing its traditional power dressing — so subtle as to be almost invisible.

The skirt became now A-line and buttoned through, so that it hung like a Sunday-morning denim number. Trouser suits, too, became more dress-down than boardroom. Skinny, ankle-cropped trousers were topped with slightly looser, hip-length tunic-jackets, a silhouette that — worn with trainers — evoked the modern weekend uniform of skinny jeans or leggings and a bottom-covering sweater. It was a look that — pricetag notwithstanding — will feel relevant to a new generation of fashion consumer.

—By arrangement with the Guardian