Sex in magazines, sex through the post, even sex at the Olympia exhibition centre in Earl's Court: it is beginning to look, this week, as though Britain is going through another sexual revolution. With the December issue of Marie Claire demanding to know whether you would "recognise your lover's most intimate parts" and the recent launch of an erotic magazine for older male readers, it seems that men and women are being targeted with equal success - and the organisers predict that thousands of visitors will have flocked to the Erotica show at Olympia by the time it closes its doors at 10 o'clock tonight.

Following the trend for more and more explicit representations of sex, Erotica has temporarily transformed the venue associated with venerable institutions such as the Ideal Home Exhibition into a paradise for voyeurs, rubber fetishists and connoisseurs of erotic prints, giving a rather different meaning to the phrase "squeeze my lemon". Instead of demonstrations of ingenious kitchen gadget, visitors are being offered erotic floorshows which include a troupe of male strippers, from a table-dancing club in Southend, where muscular men caressing their buttocks and snapping their knicker elastic to a thumping disco track is, apparently, le dernier cri.

This is a show designed for people who like basques and suspender belts, whose idea of an exciting night out is to hang around a "rude food plaza" consuming cock-a-leekie soup, and cocktails with names like Perfect Pecker and Suck and See. It's a riot of black rubber and red PVC, of soft-focus prints at inflated prices, of women giggling in hot tubs as though they're guests at a 1970s Playboy party. The relentless displays of dildos, anal wands and blow-up dolls are not so much disgusting as dispiriting, exposing the obsessions of people trapped in a time warp in which sex is always about size and performance, and women are always Girls! as in Page 3.

But does this mean that the British have at long last lost their reserve about sex? And if they have, is it a welcome development? The Social Affairs Unit, a right-of-centre think tank, believes not. In a report published on Monday, four days before Earl's Court underwent its voluntary invasion of the body-piercers, the unit denounced women's magazines for their triviality and obsession with sex. Highlighting the absence of articles on politics and bringing up children, the report claimed that the 11 titles in its survey failed to provide a positive image of women.

"Magazine Woman has escaped from the kitchen only to get as far as the bedroom," complained Kenneth Minogue, one of the report's authors and a former professor of political science at the London School of Economics. Addressing his remarks to an audience so out of touch with contemporary mores that it has apparently never seen Vogue or opened Cosmopolitan, Minogue continued disapprovingly: "The likely response to these magazines would be astonishment at the extent to which sex is king."

This may, of course, explain why so many women buy them, a point which seems to have been lost on Professor Minogue. "Magazine Woman will leave her husband or partner if she takes the slightest fancy to another man", the unit's report announces in horrified tones. "Men, for her, seem to be nothing but sex objects, to be alternately hankered over, desired, scorned or ridiculed. In short, she is as crude, offensive and unpleasant as the most obnoxious of men" - or, one might add, the laddish celebrities who rush to unveil their sexual preferences and fantasies about hot babes in men's magazines such as Loaded.

However much the Social Affairs Unit disapproves, millions of women hurry out to purchase the magazines, giving the top titles circulations in the region of half a million. Marie Claire, which has overtaken Cosmopolitan in terms of the frankness of its images and writing, is now selling 435,000 each month, putting it very nearly neck-and neck with its longer-established rival. According to the organisers of the Erotica exhibition, 40 per cent of advance ticket sales were to women even though, on Friday evening at least, most of the visitors were young men in groups, roaming from stall to stall drinking beer.

The impression all this has created of sexually liberated Britons, and especially British women, falling over themselves to acquire explicit materials and sex toys is not quite the whole picture. The Erotic Print Society, which announced earlier this month that it had launched a magazine for the more discerning customer, says that women make up only 10 per cent of its subscription list. (The magazine is sent out by post under plain cover, not to spare its readers embarrassment but to prevent copies being purloined en route.) Its target audience, according to editor, Rowan McKinnon, is a man aged between 40 and 75 who lives in the Home Counties.

Described as a magazine for retired army officers and the upper-middle class - "old farts", as one observer unkindly characterised them - the Erotic Print Society Review specialises in sexual fantasies involving women with names like Adele or "Lady Pokingham". It also displays a decided preference for what we might call historical sex, old-fashioned romps set in the 1930s or the 18th century, a time when men were men and women were - well, aristocrats or serving wenches. And serving wenches are never happier, as we all know, than when they are allowed to carry on with the ironing while being serviced - I think that's the correct verb - from behind.

Readers are inclined to send in dirty limericks and the current issue prints a letter from a Mr Richards, from Ireland, who addresses the editor as the "giver of joy and ecstasy in the twilight of my journey. Your publication is to me like swimming in a sea of honest sexual joy. Being on a pension, I cannot subscribe to many purchases," he concludes sadly. Subscribers, says Ms McKinnon, have been ringing her office from all over the country -"these absolutely charming and delightful people who say 'we're so glad to have heard about you. There really should be something like this.' I spoke to a composer for a long time this week." What her readers say when they call, apparently, is "Save us from the word sex in headlines. But they can get worked up about the word erotic."

Ms McKinnon does not use them but other adjectives such as "good" and "clean" hover around discussions of her magazine's content. Readers' preferences are summed up by an old joke, printed on the cover, which explains that "erotic is what you do with a feather; perverse involves the whole chicken". This is an altogether more traditional approach to sex than is to be found on the stands displaying nipple clamps, vibrators and PVC underwear at Olympia, where the in-your-face approach to sex is more reminiscent of the porn channels on cable TV. In-your-face but also horribly dated - with its male strippers and Page 3 girls, the Erotica show looks about as contemporary as an office outing to a nightclub in Torremolinos.

Neither the Review nor the Erotica exhibition has much in common with the agenda of the women's magazines, whose content - and especially gender politics - has a much more contemporary flavour. This brings us back to the objections raised by the Social Affairs Unit and the way in which its authors appear to have missed two important points about explicitly sexual discourse; not just its relation to fantasy, but the way in which responses to it are powerfully influenced by unconscious assumptions about sex roles.

The kind of magazines we are talking about, whether they are aimed at 30-something women or 73-year-old colonels, do not reflect their readers' day-to-day lives. If you don't believe me, here's a little test: how many women who regularly read Vogue are walking around in pounds 2,000 designer coats or hurrying off to parties in sequinned Versace dresses? (If anyone can prove to me that subscribers to the Erotic Print Society Review habitually enjoy oral sex on cricket pitches, as depicted in an advert in the current issue, then naturally I stand corrected.)

Of course the women's magazines perform a useful educative function for younger women when they write frankly about sex, but how many times does anyone need to read an article on the best way to perform fellatio? (Equally, Madonna's song "Where Life Begins" on her Erotica CD is a celebration of cunnilingus, not a guide to how to do it.) But when a right-wing think- tank starts to sound like a classic 1970s feminist critique, complaining that magazines like Elle demean women, you can bet your bottom dollar, so to speak, that something other than the ostensible target is under attack.

It is not necessary to read very far between the lines to discern an agenda that is not just prudish and pro-family but hostile to the expression of female desire. It is not as if readers lack choice; after all, there are plenty of women's magazines that run articles on how to stay married or faithful to one partner, the difficulties of combining work and motherhood, and similar serious issues - Bella and Prima, to give just two examples. What is really going on here is a visceral rejection of the idea of women as actively sexual creatures, a fin-de-siecle malaise which also surfaced in the 1890s. (The phrase "sexual anxiety" was invented by the Victorian novelist George Gissing to describe the final decades of his own century, when the spectre of the New Woman and her outrageous demands, social, political and sexual, were sending shivers down traditionalist male spines.)

The ends of centuries are peculiarly prone to outbursts of both sexual adventurousness and the kind of backlash represented by the strictures of the Social Affairs Unit against women's magazine editors who, it claims, portray their readers as "selfish, superficial and obsessed with sex". Another way of putting this would be to say that the magazines present an image of women as independent, in touch with their bodies and unashamed of the pleasure they get from sex - which is exactly what women are not supposed to be, according to antiquated but surprisingly tenacious theories about gender roles.

This is a problem whose origins stretch back to antiquity, when the philosopher Plato devoted one of his Socratic dialogues, "The Symposium", to the subject of love and desire - and allowed his characters, with the sole exception of the playwright Aristophanes, to talk as though women had nothing to do with the debate. Plato's circle was, of course, homosexual but the notion of female sexual anaesthesia has a long and depressing pedigree among heterosexual men. A woman's desire, according to the poet Samuel Taylor Coleridge in 1827, "is rarely other than for the desire of a man" - a philosophy which found its most perverse expression in the French pornographic novel, L'Histoire d'O. Written pseudonymously by a woman, the novel suggests that women are sexually submissive and have no authentic desires of their own. No wonder it received rave reviews from authors as diverse as Georges Bataille and J G Ballard, as well as becoming an underground classic.

Intelligent women from Virginia Woolf to the singer Madonna have been acutely aware of the opprobrium that rains down on women who insist on talking or writing freely about sex in a more positive way. Female novelists who wanted to write about passion were inhibited by the knowledge that men "would be shocked", Woolf wrote in 1931. "For though men sensibly allow themselves great freedom in these respects," she added, "I doubt that they realise or can control the extreme severity with which they condemn such freedom in women." (Authors of the Social Affairs Unit report, please take note.) Faced with a scathing reaction to her explicit Sex book, Madonna hit back on her following album, Bedtime Stories, with a song in which she complained: "You punished me for telling you my fantasies/I'm breaking all the rules I didn't make."

Do women feel a similar sense of transgression when they look at pictures of penises in the December issue of Marie Claire? Or when they turned up at Olympia in the last couple of days and found themselves surrounded by vibrators and plastic underwear? It is not always easy to distinguish between the easing of attitudes to sex within a culture and its commodification, which is what the Erotica show seems to be about - many of the objects on offer could easily have come from an erotic version of the Innovations catalogue, and are about as useful. And there is a danger that, with so much sexual material openly available, appetites will become jaded and there will be a demand for a return to the old taboos.

But the point about sex is that it is so closely linked to the imagination that there is room for a thousand fantasies to bloom and as many tastes to be catered for. I do not mind if retired brigadiers want to read in the Erotic Print Society Review about aphrodisiac meals - "every ingredient of my mussel soup is included to revitalise both male and female appetite and performance" - as long as women are free to go on reading about multiple orgasms in Cosmopolitan. Because the most important freedom is not that we are permitted to go out and buy sex toys at a tacky show like Erotica. It is that no one should be allowed to intimidate us into a state in which we cannot use our most important sex organs: our brains.