The bigger the better?

That cleavage is everywhere, magnified in the Tube and on the sides of buses. But do women buy the image?

This summer, breasts are big. And nowhere more so than in the current H & M Hennes campaign featuring the extremely pneumatic charms of Tyra Banks, tantalisingly encased in its Lycra swimwear range. Her figure dominates Underground hoardings and sides of double-decker buses.

This bronze uber-babe may have a gleaming white smile, flawless complexion and piercing green eyes but that's not where the million or so London commuters have been directing their gaze since the campaign started at the beginning of May. Both sexes have been struck by Ms Banks's provocative outline and ample cleavage. It's almost impossible to overlook; adorning most Tube stations magnified ten-fold and displaying the sort of decolletage that writers in "new lad' magazines would no doubt describe as ''well- stacked''.

It's easy to see why this sort of fashionable un-coverage is as attractive to men as it is to women. In the High Street Kensington branch of H & M Hennes free postcards of the campaign have, according to sales staff, been snapped up by men. ''They're always boyfriends of female shoppers,'' says one shop assistant at the Oxford Circus branch. ''Sometimes they're a bit embarrassed and the girlfriend will pick one up then make a joke of handing it over to him - he never complains.''

Few men would. But does this mean these images are aimed as much at the male's admiring glances as the female shopper's wallet? Certainly it does if one considers the central advertising proposition: buy a Hennes swimsuit or bikini and men may desire you in a similar way. This is the look they find alluring and you dream of achieving. So women want what she's got, not just what she's wearing.

Hennes is pretty cagey when it comes to discussing any aspect of female aspiration and its marketing strategy. "We don't like to be told we're part of a sexist advertising campaign," one of their spokeswomen said huffily. 'We're selling to women not men. We wanted a summer feel to our pictures. Tyra was chosen because she's young, fun-looking with an athletic figure."

She's also incredibly sexy in a hopelessly unattainable skinny-with-breasts sort of way. While girls in their early twenties may cheerfully aspire to this image, many women approaching 30 feel more weary. ''I remember seeing the poster a few weeks ago," says Jenny, aged 29, a researcher from London. ''I stopped abruptly as I got off the train. The image was really striking and I immediately thought: 'She's fantastic - so perfect I could never look like that even with plastic surgery and tons of money.' "

''Let's face it. Every man on the platform will stare at her and think 'wow' and then look at women like us and think 'oh dear'.''

Kate, aged 30, who is a teacher from Kent, also finds the pictures depressingly unrealistic. ''It's something you can't achieve. If you diet, your bosom disappears and if they're bigger than a DD cup, the chances are you're big all over.'' As the flesh quota rises, women are bound to compare their own bodies with these idealised forms and find themselves lacking. "My boyfriend always comments on those posters," says Sally, aged 28, a theatre designer. "It does irritate me in a way. She represents everything a woman should be physically - made to a male design."

Nearly all the women I spoke to about the Hennes campaign expressed admiration mingled with differing levels of envy and/or mild regret that they would never reach her level of attractiveness. Nobody was offended although the last thing they wanted to do was go out and buy a Hennes bikini. ''If you do have a big bust you know those things will fit badly - they're made for girls that are skinny everywhere - despite what she looks like in the poster,'' says Kate.

As one female friend explained: "Although I've got an average-sized bust I'm never content with it. Last year I remember wishing I could have bee- stings for breasts and now I wish I had proper big boobs. It's sad how susceptible I am to all these ads." It certainly seems to have created some confusion over the difference between sexy and fashionable. "It's a no-win situation," says Sarah, aged 32, who is a nurse. "In clothes it's still chic to be slim all over, but when you strip off you're supposed to look like Raquel Welch. How contradictory can you get? I just wish they'd use one model with big thighs, a belly and even a bit of cellulite."

Yet the advertising agencies are desperate to convince us that these images, however conflicting, are ones that women enjoy looking at - far more than men. Helen Stone, senior brand manager for Playtex Wonderbra, is adamant that the infamous Herzigova campaign was aimed exclusively at a female audience. ''We're definitely not targeting men,'' she says. ''Every single strapline is researched with women in mind. The Hello Boys ads were really about women doing it for themselves.''

But as the social commentator Peter York points out, if this was the case why didn't Wonderbra advertise solely in female magazines rather than on vast billboards? ''They're attracting men as well because they're not using a medium dominated by women. They wanted the images to be seen and talked about by everyone," he says.

Presumably so do Gossard, whose new campaign will take up more than 2,000 billboards nationwide in June. Sophie, aged 19, is the new Glossies Sheer model who appears in a skimpy black bra set, lying on her back in a verdant grass patch, gazing out submissively. ''It speaks women's language,'' gushes the spokeswoman Judy Bennett. ''It's been researched and tested among them and they love it.''

The crux of the campaign apparently rests on the strapline that will accompany Sophie's pose. Shrouded in secrecy until Wednesday, Judy can only hint at the provocative punchline. ''It's raunchy women's humour and it's not addressed to men.'' But it was written by them. ''Yes, the copywriters were male,'' concedes Gossard's marketing director Laura Cannon.

Talking to the marketing and advertising team, you'd think Gossard were lauding the benefits of a women-only consciousness-raising group, not a piece of coloured nylon. Perhaps they believe one equals the other. ''It's about generating sexuality from an inner confidence," explains Judy. ''It's not to do with defining yourself in terms of other men who say you look great.'' Hard to believe when you see Sophie prone in the grass, lips slightly parted.

If anything women are happier with the direct and cheeky honesty that has come to define the Wonderbra advertisements. They also enjoy making the most of their cleavage. ''It's heartening to see models with bigger busts. At least it's closer to how most of us look - it's not some anorexic girl with a flat chest,'' says Sarah. ''And I don't object to the assertive view of female sexuality that the ad conveys.''

Jenny agrees: ''Bra adverts have made big breasts acceptable and I'm grateful for that. The large cleavage is no longer tarty and obvious. You can show off without feeling cheap or tacky and there's a certain amount of humour involved.'' However, it's also the humour that allows advertisers a lot of leeway when it comes to relying on scantily clad women to sell their products.

A decade ago images of Tyra, Eva and now Sophie would have resided predominantly in the female arena, ie the glossy pages of Cosmo, Elle or Marie Claire. With the rise of lad culture they crossed over into male territory and became celebrities in their own right. These girls are just as likely to grace the covers of loaded, Maxim, FHM and the rest.

Now they're offered up to both sexes for universal consumption. Which comes as a blessing to advertisers who can merchandise to women but capture the boys' attention in the process. York compares this trend with The Girlie Show, a classic example of a product supposedly for women ''in control'' but quite obviously created by and appealing to men. ''It wasn't by girls for girls," he says. ''It was about girlies and fun for the lads.'' If the visual content of Gossard's new Glossies campaign is any guide, we can expect more of the same.