Sarah Brown swaps shoes as glam Sam is barefoot on the beach

She probably told herself it was all in a good cause, but whether the cause that attracted her to a celebrity heavy girly "accessory swap shop" at the home of Australian author Kathy Lette was raising money for charity or to assist her husband's desperate political plight, only Sarah Brown will know.

The Prime Minister's wife is also fighting the challenge from the Tory leader's stylish wife Samantha Cameron, who is today pictured barefoot with her husband David on a Cornish beach, in what could easily be mistaken for a Boden catalogue shoot.

Mrs Brown went to Lette's north London home to swap some under-used accessories at £10 a time in aid of Cancer Backup, an event organised by Good Housekeeping magazine.

Those present at Lette's home to fight over Mrs Brown's Stella McCartney shoes - worn once to the British Fashion Awards and therefore, she told the Times, "doomed" never to be seen in public again - included television presenters Penny Smith and June Sarpong, writers Lynda La Plante and Fay Weldon, impressionist Ronni Ancona and singer Dannii Minogue.

Mrs Brown made it clear that when it comes to dressing she is reconciled to finding a middle road between excess and frumpiness.

"I didn't stand a chance, did I?" she said of her recent encounter with Carla Bruni, wife of the French President Nicolas Sarkozy.

"I was standing next to a supermodel. I thought whatever I wore wouldn't matter."

The Browns are currently on holiday with their two sons in Suffolk and have visited a country park in Norfolk.