No, no, Samantha Cameron. Not the “fashion” dress. Not in the country, not at your son’s christening, surrounded by real people, who cannot tell their Balenciaga from their Bhs, let alone their Belstaff. I think you all know the frock to which I am referring. Yes, the Marc by Marc Jacobs with the silk panels (or, to the uninitiated, a dowdy blue dress with an apron attached).

It was a schoolgirl error – surprising, given that Cameron is the creative director of Smythson, and a woman of taste and substance. Marc Jacobs for London fashion week, yes; for a weekend in Rock, no. Marc Jacobs for Voguette cocktails in Notting Hill, yes; for a Tory fundraiser ball, no. In a very fashionable context, very now; in a regular, everyday context, very Maria in The Sound of Music, just before her employment by Captain Georg von Trapp.

It’s no secret that there are fashionable clothes (for us) and then there is “fashion”, which is right at the needle tip and strictly for advertising, celebrities and girls who work in the industry. It’s that Chloé patchwork dress (or pretty much any Chloé dress). It’s those McQueen PVC trousers. Those clothes are meant to make you think, first: the designer’s name. Then: “How much?” And finally: “Best leave that to Sienna. I’ll settle for the bag.”

Ordinary civilians aren’t meant to buy this stuff, because they cannot hope to carry it off. That is why the “fashion” houses do shoes and accessories – so that regular grown-ups can get a look-in without making fools of themselves. The Marc Jacobs collections are made for Kirsten Dunst and her friends, to be accessorised with white ribbed tights, ankle boots, trapper’s hat and rock-star boyfriend. These clothes require you to be young, quirky, edgy, stylish – not even fame or good looks guarantee that you can wear “fashion”. Remember Céline Dion in that back-to-front John Galliano tuxedo and trilby? Or Geri Halliwell in the Versace chiffon jungle number? Come to that, think of Posh any day of the week in any one of her black-and-white hostess outfits. Horrible.

But it is tough on civilians in Cameron’s position, and nobody wants her to enter the no man’s land of Clothes Worn by Politicians’ Wives. Perhaps she could take a leaf out of Gwyneth Paltrow’s book – another high-profile mother of small children, also London-based. Think fashion-conscious, but not victim (a bit of simple Balenciaga, nice jeans, good sunglasses, Chloé Héloise bag).

I suggest Cameron gets her “fashion” hit the way the rest of us do – in the places where it’s easiest. Those Burberry patent ankle boots are nice.

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