Come on Sarah, you can compete with Carla

Obviously, I am greatly troubled by the outlook for the world economy, but I'm far more troubled by the outlook for Michelle Obama's arms. London in April - it's not exactly weather for a shift dress, is it? Yet Mrs O's taut, toned arms have come to be her trademark, the sleeveless dresses that set them off a key component of her signature style. Imagining Michelle without bare arms is like imagining Carla Bruni without her cheekbones: a photo op too banal to contemplate.

But while the biggest conundrum facing Mrs Obama is whether or not to risk goosepimples, Sarah Brown has far more pressing concerns. That her husband has presided over the biggest financial crisis to hit Britain since the Thirties must be hard enough. That her husband requires her to stand in the same room as Carla Bruni is the bigger deal breaker. Mrs Brown looks lovely in her smart grey suits, and by any other benchmark would be judged as stylish. But nobody short of a supermodel could fail to come off badly when compared to a woman who is, let us not forget, a former supermodel.

In addition, Mrs Sarkozy is wardrobed by Christian Dior, and wears the finest brands in the LVMH firmament. She has no qualms about wearing diamonds, this season's It bag or a floor-length ballgown by Yves Saint Laurent. Crucially, she is allowed to do so by the French, who, while they may set fire to tyres and lock people in offices in protest against perceived economic injustice, are fairly magnanimous about their heads of state wearing expensive designer clothes.

Compare this to Mrs Brown, who would get lynched for wearing any designer label, British or otherwise, and whose most positive press came about as a direct result of wearing a £7 beret from New Look. Glancing tremulously in the mirror this morning, smoothing her suit, nobody could blame Mrs Brown for darkly muttering: "well, what do you expect for £59.99?"

Mrs Brown may not wish to assume the role of brand ambassador for the Britain fashion industry - and who can blame her. But this is the way that politics is going, with increasing focus on the wardrobes of the first ladies as an antidote to fiscal gloom. Mrs Obama and Mrs Sarkozy promote their own designers tirelessly. To borrow a favourite phrase from The Apprentice, Mrs Brown needs to step up to the plate. And make sure said plate is more Royal Worcester than Reject Shop.