YOU MUST remember this - a kiss is just a kiss . . . in Japan, however, a kiss is far from a simple matter. Recently Japanese have been scandalised by the latest phenomenon to sweep their hi-tech, 2lst-century country - kissing on the street. Not just onthe street, moreover, but on the train, on station platforms, in the park . . . And we are not talking polite peck but serious deep-throat smooching.

The practitioners are mainly in their teens and early twenties. Mariko Kojima, a 21-year-old, is a student and enthusiastic skier. Her bedroom walls are covered not with pictures of singers or hunky young men but with close-ups of couples kissing. "When I'm out with my boyfriend," she says, "I don't think about other people. If I want to kiss him, I kiss him. There's nothing wrong with kissing in public - that's what I think, anyway. We're not doing any harm."

Mariko's mother thinks otherwise - as does almost every other member of her generation. Recently there has been a rash of television programmes and articles, all relaying shock and outrage. "Haven't they got any morals?" demanded people on the street in a TV Asahi programme on current affairs. "Kissing in public - it's ugly!" trumpeted social commentator Chiaki Aso in the weekly magazine Shukan Yomiuri. "These people never give a thought to how others feel, the people who have to see them do it."

"People kiss on the street abroad," shrugs Mariko. "We're just getting more Westernised." Certainly the fad seems to have begun with television and with Western movies that show scenes of passionate kissing. Students of the trend in Japan date it back more specifically to a television commercial put out by the cosmetics manufacturer Kose Corp in autumn 1992, for a new brand of foundation.

This features an assertive young woman, very different from the traditionally coy Japanese girl, who turns to her boyfriend and demands, "Ne, chu shi te! Kiss me!" He hesitates. "Kiss me, kiss me!" she insists. He does. Everyone remembers the image - andthe phrase. "Chu shi te!" was awarded the prize for Most Memorable Phrase of the Year. "We started a trend," says a spokeswoman for Kose.

Since then the fad has taken off. Men's magazines run features on the cool way to kiss in public. "Give your partner a casual embrace and a light kiss on the lips," advises Popeye magazine. "Never a deep kiss or fondling." This year Shiseido, the make-upmanufacturer, brought out a smudge-free lipstick, guaranteed to withstand repeated kisses and not to smear the partner's collar. It also carried out a survey of 400 Japanese men aged from 18 to 44, and discovered that 29 per cent had kissed a woman "on a station platform, in a train or on the pavement"; of those, 57 per cent said they had felt embarrassed.

And the Global Report on Dating revealed that although 30 per cent of Japanese women would most like to go out with a sexy stranger (in contrast to 12 per cent of women worldwide) and only 20 per cent would prefer their husbands (47 per cent worldwide), only 2 per cent said it was okay to kiss in public (in contrast to 55 per cent of women worldwide).

As anyone who has ever been to Japan will remark, all this seems a bit strange. It is a land, after all, where the sex industry, though illegal, is healthy and thriving, where men read pornographic manga comics openly in the subway, and where it is inadvisable for the easily shocked newcomer to turn on the television after midnight.

Until last year it was illegal to show pubic hair in images, which resulted in much touching up of imported films and magazines. Then the ban was lifted. The result was what Japan refers to as the Hair Boom. Actresses and singers of all ages, from Japan'

s equivalent of Glenda Jackson on, rushed to publish volumes of nude photographs of themselves.

The boom goes on. Today it is still nearly impossible to open a magazine, even the serious, heavyweight titles, without being confronted with pictures of naked women, pubic hair and all.

So why all the fuss about kissing? For a start, the kiss in Japan is a far more erotic activity than it often is in the West. People do not routinely greet friends and relatives with a peck on the cheek. Even soldiers returning from a long tour of duty abroad get no more than a smile and a bow from their wives on arrival at the airport.

The kiss, in fact, is not a part of traditional Asian culture (nor, for that matter, of African custom). It is closely tied in with European notions of romance and courtly love, according to which love and marriage "go together like a horse and carriage". As an early visitor to Japan wrote in 1888, "Love, as we understand the word, is a thing unknown to the Far East." In Japan traditionally there was marriage, a socially approved bond between two members of the same class, with the purpose of producing progeny; and recreational sex, with professionals. Occasionally, an unfortunate might fall in love, usually with a geisha. The result was very often joint suicide ("love suicide").

Kissing arrived in Japan with Westernisation; the first Japanese to witness public kissing were as bemused as if they were seeing Eskimos rubbing noses. In the l930s, when there was a proposal to exhibit Rodin's The Kiss in Tokyo, there was outrage. The police banned it. Some people suggested that the naked sculpture could be shown just so long as the heads were wrapped in a cloth, so that no one would see the offensive kissing. In the end the Rodin was not shown until after the Second World War, which was also when the first kiss occurred in a Japanese film.

Nowadays the Japanese are perfectly au fait with kissing. Kissing is fine - so long as it stays where it belongs, in the bedroom. The real problem with the public kiss is that it is public.

Showing affection in public, in fact, goes so much against the grain that it has set alarm bells ringing. "Is this the end of the shame culture in Japan?" shrilled a recent headline in the Nikkei, Japan's equivalent of the British Financial Times. In Japan, as a "shame culture", the chief restraint on bad conduct is fear of being shamed in front of others, of losing face. We, conversely, are a "guilt culture", wracked by guilt even if no one knows that we have committed an offence.

Young people kissing in public are no longer afraid of what people think of them; they have lost their sense of shame. But if shame is the underpinning of Japanese culture, without it this public kissing may signal the end of civilisation as the Japaneseknow it. As Shizue Tsutsumi, a 43-year-old woman, wrote in a letter to the Yomiuri Shimbun newspaper, "Without shame, there is no sense of restraint. If we lose that, we're no different from animals."

For Mariko and her generation the question is not so apocalyptic. "I kiss my boyfriend because I love him," she says. "What's so special about that?"

"The Japanese," wrote an early visitor in 1916, "are sufficiently delicate-minded not to make love in the streets and frighten the horses; nor do they ever, under any circumstances, sit in couples in their parks, glued to each others' lips." Things have certainly changed since his day.

Lesley Downer is the author of `The Brothers: The Saga of the Richest Family in Japan', published last month by Chatto & Windus, £20.