Sarah Sands: Why Mariella's pillow talk is front-page news

Whatever Mariella Frostrup's strong views on Liberia or the Orange Prize, they cannot compete with the engulfing tide of interest in her bra-wearing habits. The word "bra", like "Israel" or "Palestine", triggers a global meltdown on the internet.

When The Daily Telegraph ventured into digital television some years ago, it had an early epic success with one of its fashion reporters being fitted with a Rigby and Peller bra. I doubt that it ever came near to those royal wedding-style viewing figures again. No wonder Mariella's bra was a front-page story for the paper on Friday.

I couldn't altogether judge the visual resonance of the story that Mariella had followed Paul Yates's advice and worn a bra in bed for 15 years. Is this considered by male readers to be a lusty challenge, or an obstacle? Do they hope that it is part of a full kit of stockings, suspenders etc, which every self-respecting television presenter should sleep in?

Although I swear that I spotted a nipple in a recent edition of the Daily Mail, and wonder if the editor noticed it too, underwear is the final frontier for most family newspapers. So they make the most of it. Christmas, Valentine's Day, anniversaries and Cameron mini-breaks are all occasions to get the lingerie pictures out.

Middle-market heroines are not naked, but women in their underwear or bikinis. Elle Macpherson, Kylie Minogue, Liz Hurley and anyone from Victoria's Secret. Footballers may bring home glamour models, but social mobility leads to thongs.

The Oxfordshire "lord of the manor" Kevin Cash, who fell out so publicly with his butler and housekeeper recently, was married to an underwear model 18 years his junior. Kerching. Even Kate Middleton first came to the notice of her future husband, Prince William, by appearing in her underwear at a university fashion show.

Distressingly, the television news reporter Lara Logan has not been able to forget her past job as swimwear model. When she was sexually assaulted while reporting on the protests in Egypt, some bloggers speculated that she had brought it upon herself.

Ever since Mary Phelps Jacobs invented the modern bra in 1913, in order to make women more comfortable, it has been a source of wonder to men. They love to calculate the mind-boggling combination of alphabet and numbers. I remember explaining to some young men Nigella Lawson's rare statistics; a narrow back and fabulous bosoms means she is something like 32GG.

Meanwhile, a favourite fact in the press is that very few women wear properly fitting bras. Bra fitting is a science, requiring a female version of Brian Cox to master and teach it.

There is a generation, mostly Tory MPs, even more Neanderthal than David Willetts, who still refer to feminists as " bra burners". Men buying lingerie claim to know nothing of the engineering purpose of bras but have an atavistic fear that women who don't wear them will turn into harpies.

I emailed Mariella to tell her I am writing on a subject of national importance and would appreciate any guidance. Her response was spirited. She was referring to Paula Yates wearing a bra in bed, not to herself: "I wear flannel pjs and a vest, def not fantasy bedwear." Tread gently, Mariella, for you tread on our dreams. I bet Fiona Bruce sleeps in top-to-toe leather.

Sarah Sands is deputy editor of the 'London Evening Standard'