Twenty years ago, 10 years ago, even five years ago, it wouldn't have sounded promising. Picture the scene: you are a brand manager of an 'over shoulder boulder holder' renowned for 'lifting and separating'. You are competing with bras that thrust the bust heavenwards and use the pneumatic body of a nubile blonde to advertise the fact. But your customers find that kind of imagery offensive, degrading, sexist and cheap, writes Marion Hume.

Yet as you fret over how to give your hard-working, supportive and practical bra 'oomph', some creative type across the boardroom table is talking about enlisting the natural body of an untucked, unlifted woman who turned 50 last November. Madness]

And so it would have been, before Lauren Hutton grew up. For Hutton, and the legions of women to whom the model-actress-activist is a standard-bearer, has refused to give in and grow old quietly. Hutton, and women like her, have forced a redefinition of what women at any given age are supposed to look like.

'This may be the peak of my life. Why shouldn't I look like it is?' says Hutton, newly signed up to promote Playtex Cross Your Heart bras. Her voice amplifies those of less well-known women who refuse to be cowed by age or ubiquitous images of beautiful youth. 'What was I supposed to do with my breasts when I turned 50, send them off to the country?'

Playtex is 'thrilled with Lauren Hutton because she is admired by women of all ages', says Fiona Hubert, marketing manager. Indeed she is - in part because of a gritty, glorious sexiness, and in part because she is the perfect antidote right now to the waifs and schoolgirls in teeny-weeny dresses and knee-high socks.

These have their place in the fashion spectrum, but appeal not one iota to the bulk of the female population. 'And why should they?' says Hutton. 'I wouldn't wear now what I wore as a girl, because I'm aware of my sexual potency in a way I wasn't then. The body of a girl is like a gun with the safety catch off. But you don't know that at the time. Now, as a grown woman, I'm certainly not afraid of my fire power.'

But she was none the less an odd choice for Playtex, whose offer she initially turned down because she doesn't usually wear a bra. She favours singlets with nothing underneath, 'which started in the Sixties, with our quest for pussy power. But you know what? Men really love bras. As a woman who doesn't always wear one, it's fun to put one on and see them stare]'

It is also profitable. Hutton changed her mind and said yes so that she could earn the dollars 50,000 for these pictures and give it all, every cent, to breast-cancer charities, so turning the deal 'into something that would work for us'. By 'us', Hutton means womankind, on whose behalf she has a misson. She said yes to Playtex and then insisted that the link with breast cancer be mentioned in all publicity.

This is not the established way to sell bras. Manufacturers market products on sexual allure. To them, the bosom is an erogenous zone to adorn. But to women, it is also where fear lurks. In the UK, where Hutton will give half her fee to a breast-cancer charity, the disease kills 15,000 women every year. (She has already given the other half to America's National Breast Cancer Coalition.)

Commendably, the bra giant is not only thrilled with Lauren Hutton, it is proud to be associated with her mission. When Hutton finished posing in all the varieties of Cross Your Heart bras and then turned round and asked, 'But what have you got for women less healthy than me?' Ms Hubert didn't run scared. She points out that while the Cross Your Heart bra is not primarily designed for women who have had a mastectomy, 'there are bras within the range that women wearing prostheses can feel confident in, because the cups are formed in such a way that these would be held firmly in place.' She adds that 'Playtex are looking at launching a pretty and feminine bra collection specifically for women who have had a mastectomy.'

Primarily, the message that Playtex wants to get across via Hutton is that bras are sexy, whatever age or size you are (the Cross Your Heart is available from a 32 up to a 42DD, and a new all-over black lace version has been introduced for larger sizes).

Meanwhile, the fashion message is that bras are also more in vogue than they have ever been. In fashion terms, the bra has been transformed from a piece of underwear to a serious component in the visible wardrobe.

Much of this is to do with the phenomenal success of the Wonderbra, although bras worn 'Hutton-style' - spied under a jacket, or glimpsed in fresh white cotton above the cut of a floral dress - will be judged by many women to be more relaxed and more womanly. Designer style goes a step further: for autumn, expect to see antique dark versions incorporated into dreamy dresses and neon-bright varieties visible under pastel shirts.

The bra promises to have a subtle but starring role at Karl Lagerfeld's haute couture collection for Chanel, to be shown in Paris next month. He revealed to me last week that he has recut his jackets with the tiniest shoulders and moved the padding down to the side of the breasts, Wonderbra style, 'because it's the biggest thing in fashion. It has influenced the shape of clothing even more than the shoulder pad. It gives a beautiful shape,' he says.

So everybody's up to it. But trust Lauren Hutton to be up to it with both a come-hither smile and a conscience.

Playtex Cross Your Heart bras are available from Debenhams, Oxford Street, London W1, and branches; House of Fraser, John Lewis and Contessa branches nationwide.

(Photographs omitted)