If their calculations are correct, the sentence “rainen no kono hi mo issho ni waratteiyoh” will spark a new era of unbridled romance in Japan: it is, according to hours of meticulous psychological and sociological research, the ultimate chat-up line.

Directly translated, the killer phrase is: “This time next year, let’s be laughing together.”

The chat-up line draws its incredible potency from three powerful “word triggers” that work on a subconscious level to make their target go weak at the knees. Individually, each word is good; together they are irresistible.

The ten-strong panel, whose final deliberations were covered on Japanese evening television, included university professors and medical psychologists and, for good measure, Takaaki Ishibashi, a veteran television star who has heard thousands of lines — both great and truly awful — in two decades of presenting Neruton, Japan’s equivalent of Blind Date.

As they honed the sentence to its final form, the emphasis fell on two critical factors. The first was the words themselves. Use of the phrase “this time next year”, one of the panelists explained, sends a cunning sign that the chatter is interested in more than just a fleeting moment with the chattee, setting up the subconscious possibility of long-term love.

Similarly, the word for “together” suggests that even after a year of dating, the joy of each other’s company would still be fresh. The use of the word “laughing” then cleverly softens the whole phrase, repeating the “mutual happiness” trigger but suggesting cheekiness, a sense of humour and a general lightness of heart. The phrase’s second secret weapon is its lack of sleaziness and, according to its inventors, the great difficulty in responding to it with an outright brush-off. It insists on nothing, it starts a conversation going and its simplicity means that it can trip off the tongue of even the shyest Romeo.

The discovery comes in the nick of time for Japan, whose fertility rate continues to lurch downwards to record lows. Observers have spotted numerous signs that Japanese romantic life is taking a beating from long working hours and the nervousness of men around increasingly successful women. Incidents of women buying pets has quadrupled over the past year and occupancy rates at the country’s 18,000 “love hotels” have plummeted.

The chat-up line is for any context, but it favours particular situations. It works extremely well, for example, if used to chat up someone you have seen a few times in the office but never spoken to. It is good for the coffee shops, but less effective in noisy bars.

Its perfect application would be in Japan’s many “pulling places” — spots in each town where, by tacit public agreement, any woman who pauses for more than a few seconds is fair game.

. . . BUT THEN AGAIN, MAYBE NOT

Rachel Harrup, 36, an English teacher from Bath:

“Even if he looked like George Clooney, I would run a mile. It might be effective in Japanese, but I think British women prefer something more jokey or straightforward, such as: “Can I buy you a drink?”

Sarah Burton, 32, a musician from Bury St Edmunds:

“The Japanese should stick to inventing gadgets if that’s the best they can come up with.”

Laura Gibson, 29, a public relations executive from Bristol:

“The Japanese population will die out if all the men resort to this line. It sounds like a line designed by men who have no sense of humour and who think that all women are stupid and desperate.”

Alison Hunt, 36, a writer from North London:

“It would fall completely and utterly flat. It’s quite creepy and you’d have to be really desperate to go for it. I think British women prefer a more subtle, light-hearted approach.”

Jen Barnes, 38, a social worker from East London:

“I would assume he did not have a good grasp of the English language. It’s too formal and a bit scary.”

Zoe Ellis, 40, a television executive from North London:

“I would reply: ‘Why not now, cos I ain’t laughing?’ And walk off.”

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