Of all the cruel sartorial fates that a woman might endure, the opportunity to be photographed standing next to a supermodel is not one that many would welcome. Especially when that supermodel happens to be in around £7,000 of double-faced Dior cashmere and you are wearing a crumpled, off-the-peg white jacket, which plays havoc with your pallor.

Such was the fate of the PM’s wife, Sarah Brown, when she held a luncheon for Carla Bruni Sarkozy yesterday in St James’s, London, with 150 female guests including Emma Freud, Judi Dench, Annie Lennox and Sabrina Guinness.

The fashion tension was palpable. Go too trussed up and you might appear as if you were trying to compete, too toned down and you might blend into the background. In the end the hair was big, the coats’ fur trims were even bigger. But, bar a few exceptions such as a slick grey trouser suit (not too dissimilar to Mrs Sarkozy’s), the rest of them appeared to be a motley crew with no discernible “wow” factor.

Sarah Brown’s former career as a PR consultant would certainly have impressed upon her the importance of a camera-friendly statement outfit. Certainly there was nothing wrong in going to Jaeger, a premium high street brand which is renowned for its tailored, classic approach to fashion. But it was a mistake to choose monochromatic shades. Her choice of white jacket (a careful, three-figure £299) did not help slim her silhouette and the black dress was ageing. However, the opaque tights were a triumph of sorts; not everyone can pull off 10 denier the way Mrs Sarkozy can. Perfect, toned and wrinkle-free legs are certainly a requirement.

The choice of jacket fabric was also unfortunate: when you know you are going to be subjected to the harsh glare of the paparazzo’s flash, cotton can often possess the unflattering sheen of something that has faded in the wash.

There is a pathetic expectation in this country that Sarah Brown should dress as a woman of “the people” when actually she is the PM’s wife, who should have got herself kitted out in something with a luxe finish: a tweed, perhaps, to keep her warm, or a wool or silk jersey, which would have at least hung properly.

Unsurprisingly, given Mrs Sarkozy’s access to Dior’s autumn/winter collection, she managed to look sufficiently “on trend” in her fashionable choice of purple and grey, as well as elegant and pulled together. In her trouser suit, she even appeared a little dynamic. In another canny move (not much, one assumes, was left to chance for this trip), none of these Dior items will be sold until May or June, thereby ensuring that these outfits were being worn for the first time. It is a coup for the French fashion house, whose sales will undoubtedly rocket off the back off the endless press coverage Mrs Sarkozy has received this week. So lucky for those invited who could not make it to the lunch, and the subsequent unfavourable comparisons that will follow. But then, unless you are a Rolling Stone, how many times in your life do you have to stand next to a supermodel?

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