The hired guests at the wedding

Kenichi and Toshiko's wedding, everyone agreed, went like a dream. In a hired banquet hall in a Tokyo hotel, the assembled relatives and friends ate sumptuously, mingled amicably and reflected on the future of the young salaryman and his bride. At the high point of the reception, a beautifully dressed lady stepped up to the microphone with a sentimental glance at the happy couple.

"Toshi-san, Ken-san - sincerest congratulations!" gushed the woman, introduced as a friend from the bride's company. "I have to admit that I'm a teeny bit jealous, but I wish you happiness from the bottom of my heart." Cheers, laughter, and wet hankies.

But all was not what it seemed. When the banquet ended, and the guests were rounded up for a post-reception drink, the elegant lady politely declined. Toshiko's other workmates also left in rather a hurry, and for a very simple reason. Far from being friends and colleagues, they were all paid actors, specially hired for the occasion as part of an elaborate cover-up.

The man behind the deception was Mototoshi Kakizaki, a 34-year-old former software engineer who started his company, Zipangu, eight years ago, to cash in on the booming weddings industry. Originally his services were more straightforward, limited to ghost writing the interminable speeches without which no Japanese wedding reception is complete. A nervous toastmaster would occasionally ask Mr Kakizaki to provide a stand-in, and it was from here that he hatched the idea of supplying rented guests.

Business boomed: as the market leader in a field of half a dozen similar companies, Zipangu nowadays retains a stable of 150 amateur actors to play the parts of friends, colleagues, bosses, university professors and teachers, even siblings and parents. As the summer wedding season gets under way, he expects to cast more than 20 such occasions.

"People come to us for various reasons," he says. "Sometimes they've got several marriages behind them, and they're simply embarrassed to be calling up their friends for the third or fourth time. Some companies ban marriage between their employees, so they'll hire 'colleagues' to keep it a secret. Then there are people who've fallen out with their parents over money, or just people from the provinces who want to impress the folks back home."

One Japanese bride invented an Oxford education and a brilliant career in the prestigious Ministry of Finance and cast her reception accordingly. The circumstances of "Toshiko" are more common: after moving to Tokyo from her home in the sticks, she found lucrative employment as an "entertainment worker" in Tokyo's thriving sex industry. She met "Kenichi" when he availed himself of her services. All this was considered too complicated to explain to her elderly parents.

Rented acquaintances do not come cheap, although their cost varies depending on the complexity and exposure of their role. Fake colleagues, with no speeches to give and few duties other than deflecting inquisitive questions, begin at around 30,000 yen (pounds 190), plus travel expenses. "Old friends of the family," who might have to give toasts, deliver long sentimental reminiscences and keep up the pretence over months of excruciatingly formal engagement ceremonies and getting-to-know you sessions, might cost 10 or 20 times as much.

The stresses of pulling off a pseudo-wedding are considerable, although Mr Kakizaki is proud to say that Zipangu has never been caught out. "There's a great sense of satisfaction in helping people, and easing their anxieties," he says. "In years to come, they will watch the video of their wedding. Without fake guests, their relatives might say, 'Oh, she doesn't have many friends, does she?' We have saved them from that miserable situation."

Zipangu is the most bizarre of a vast number of companies devoted to fulfilling the exacting criteria of Japanese weddings. About 800,000 couples will marry this year; according to a survey by Sanwa Bank, the average wedding costs 3m yen. The prime beneficiaries are city hotels and "wedding halls" which offer packages combining a ceremony - Shinto, Buddhist or Christian - reception banquet and gifts (in Japan, the couple present their guests with goodies; in return they receive envelopes containing crisp 10,000 yen notes, worth around pounds 60 each).

But this is threatened by a troubling demographic trend. By nature, baby boys outnumber girls by about 105 to 100, but the imbalance used to even out because of the susceptibility of boys to childhood diseases. Improved medical care has preserved the surplus; improved access to careers and education for women has enabled more of them to remain financially independent and single. The result is that, among unmarried Japanese in their twenties and thirties, there are 1.4 times as many men as women.

The consequences of this are examined by Naohiro Yashiro, an economics professor at Tokyo's Sophia University, in his book The Economics of Marriage. Men and women in Japan, says Prof Yashiro, have traditionally selected their mates for drastically different reasons. "For a man, the main motive is social status - by the age of 30 or 32, employees in most big companies are forced to marry, otherwise their prospects for promotion are jeopardised."

For the girls, however, marriage is "an economic activity", according to the professor. "An economic activity is any situation in which, within given constraints, you try to maximise your satisfaction. For most people, for instance, money is very scarce, and you struggle to get maximum value out of it. But love and marriage also have their limitations - your attractiveness, education, income. Within these limits, you try to make the best marriage you can."

A Japanese saying has it that "For women, marriage is lifetime employment." Twenty-five years ago, that was true: the mean age of brides was 23. But now, in the unromantic analysis of Prof Yashiro, "since women have become more financially independent, they no longer have to 'sell' themselves at low prices. Economically speaking, it is very rational to stay single until one finds the right person."

Illegitimacy is very rare in Japan so, as women marry later (the mean age is now around 26), their child-bearing careers are shortened: the average number of children per mother is now less than 1.5. This has worrying consequences for Japan's future labour market and tax income. But it also means that three out of every 10 men under 30 will be unable to find a bride. The problem is especially acute in the big cities. In Tokyo, 10 per cent of 50-year-olds are confirmed bachelors, and thousands of marriage agencies have sprung up, many of them specialising in introductions to Filipinas, Koreans, Chinese or Russians.

It is this urban alienation that explains the success of Zipangu's rental guest service, believes Mr Kakizaki."Japan has all these social problems now," he says. "Young girls coming to the city to work as prostitutes, divorces, children falling out with their parents. But people still want to have a traditional wedding, and we help to fill in the gap in their lives. Everyday life in Japan looks so westernised from the outside. But when it comes to marriage, there's much more to it than meets the eye."