How low can she go?

Britney Spears has become as famous for her fashion faux pas as her hit singles.

And now she's done it again. The American pop star appeared on stage wearing trousers so low-cut at the front that they revealed almost a full inch of her purple underwear.

It was as she rehearsed for a performance at last night's MTV event in New York that the 21-year-old showed off perhaps more than she intended. One MTV insider said: 'Rather than looking cool, the sight of her underwear at the front had most of the crews on set sniggering.'

Increasingly low- cut ' hipster' trousers have long been a fashion accessory favoured by female stars including Jennifer Lopez, Christina Aguilera and Beyonce Knowles.

It is not the first time Miss Spears has grabbed the wrong kind of headlines with her dubious grasp of style.

Two months ago her appearance at a New York party in thigh-high leather boots and stripey sweater dress was derided by fashion experts.

And in June she attracted similar criticism after combining a diamante bow-tie necklace with an off-the-shoulder T-shirt, trilby and black stilettos.

Other eyebrow-raising outfits have included a leather bondage-style creation and a cleavage-revealing orange and purple dress.