Carla Bruni-Sarkozy has handed Christian Dior, the Parisian fashion house, a £1m advertising gift better than any of her magazine covers or catwalk shows by being a walking billboard for its clothes in London last week.

Political opponents of her husband believe they can detect the subtle hand of Bernard Arnault, France’s richest businessman with a personal fortune of £13 billion, in helping to give one of his companies a boost through his good friend, the president.

What better way to revive Dior’s interests after its autumn prêt-à-porter collection took a drubbing from critics at last month’s Paris fashion week than to have France’s first lady glide down a runway that stretched from Heathrow to Windsor Castle, the City of London and Greenwich.

The new collection, the handiwork of John Galliano, the British fashion designer, was dismissed a month ago by the influential Cathy Horyn of The New York Times as “a throwback to an era of luncheon suits, helmet hair and little gloves”. But since Bruni arrived in London wearing a calf-length Dior coat, beret and the fashion house’s name writ large on her pumps, it has taken on a new cachet. One fashion industry source suggested the exposure the collection received would be worth £1m in extra sales.

Even Justine Mills, owner of Cricket, the Liverpool boutique beloved of the city’s football Wags, who once said she would not stock Dior because she imagined the people who bought it were “Russian prostitutes”, has had a change of heart. “Dior has changed its direction for the better,” she said. “It is much more understated and about luxury and quality.”

The question on many fashionistas’ lips is: will Carla get to keep her new £30,000 wardrobe? Four spokeswomen at Dior said they did not know if the clothes were a gift. The Elysée Palace declined to comment.

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