So many people here turn for help to professional couple-busters who offer to end a relationship with the minimum of friction, fuss and embarrassment.

The professionals, who do not come cheap, are known in Japanese as wakarasase-ya, which literally means “separator”. They are often private investigators who have switched to this line of work because of the high demand.

About 80 per cent of customers are young women, mostly from well-to-do families. Typically, she has become involved with a man, finds out that he is not her type, and is then anxious to break off the relationship cleanly so that she can continue the search for Mr Right. Osamu Ohta, head of Imperial Life Research, describes the modus operandi in a fairly typical case that his agency handled recently. A young woman could not shake off a boyfriend who was preventing her from forming a new relationship with a better marriage prospect.

“I assigned a female agent familiar with the target’s (boyfriend’s) line of work, and she approached him disguised as a businesswoman,” Mr Ohta said. “The operative won his trust and they became friends, but the target didn’t show much interest in her. At that point the agent introduced a friend and the three went to a karaoke bar together.”

This new, attractive friend diverted the target’s interest away from the client. They went on dates — until the client stopped paying the fees. By then the client was satisfied that the irksome boyfriend was off her back.

“At that point the new woman friend made excuses about having to work late at night every time the target asked her out. She, and the agent in charge, were pulled off the case,” Mr Ohta said. “The case took a month and was a success.”

He claims an 80 to 90 per cent success rate in breaking up couples. Mr Ohta’s company has expanded rapidly, with 70 franchise outlets across Japan and 100 agents, handling between 500 and 600 cases a year. Couple-busting is one of the few business sectors flourishing in Japan’s stagnant economy.

The success of the couple-busters is based on cultural peculiarities. The Japanese language has countless ways of saying “no” without actually using the word “no”, and people often prefer to shun direct assertions and speak in circumlocutions.

Hiring a professional is sometimes the least troublesome way of making your meaning clear and of avoiding an embarrassing scene. The charges are steep, however. Hiring these professional busybodies for a month costs about £4,400 at Imperial Life Research.

Sometimes the methods used by cheaper couple-busters are less than delicate. Those familiar with the business say that less reputable outfits often use threats.

For an advance fee of 30,000 to 200,000 yen (£170 to £1,100) some couple-busters adopt a direct approach — no pussyfooting about using a decoy to befriend the target as the reputable agencies do.

Everything is much simpler if the target holds a good position in a large company or in a government office, which makes him vulnerable to blackmail. It may be enough for a bullying stranger merely to telephone the target and hint that his boss may hear about his subordinate’s “stalking” activities.

“This kind of thing gives the profession a bad name,” Mr Ohta said.