"Japan syndrome" hits about 10 Japanese tourists to Paris a year. The victims are so disappointed at the dirty streets and rude waiters that they succumb to a nervous breakdown at the idea of having wasted a week of leave and savings on a trip to the City of Lights.

There is said to be a psychologist, Japanese of course, who treats these despondent compatriots at the embassy. So when I read about a group of Japanese volunteers who gather once a month to clean the famously cobbled streets of Paris I saw a story.

Place de la Concorde is a busy intersection of ferocious drivers in underpowered cars hurtling past some of the most beautiful architecture in the city. At the epicentre I find a group of 20 Japanese dressed in green tops holding tongs and brooms, with cameras and gloves, waiting for their leader Osamu-san to start the slow march up the Champs Elysees.

I interview Osamu-san. It is stunted and in three languages. His reasons for the group's existence seem not to require explanation: Paris could be cleaner and so the group is cleaning it up. Simple. "Green Bird - Keep Clean, Keep Green" read their vests. "It's not so clean in Osaka, either" he says smiling, not wanting to appear superior.

So up the Champs Elysees we go, stooping to pick up cigarette butts and old metro tickets. This isn't exactly Jakarta, but the quantity of rubbish that fills their bags is astonishing. A street-cleaning truck drives past, its driver watching quizzically as two housewives sweep the beige sand of the walkway.

I wasn't the only journalist on the scene and every move is photographed, questioned by the six other journalists. The Japanese just carry on stoically, oblivious to the camera shutters clicking, posing politely.

It is a cool Sunday afternoon and the passers-by watch our group with amused haughtiness. Japanese tourists take photos, the Americans ask questions, the French don't break stride.

After 200 metres up les Champs the adventure is over. Osamu-san pulls out his hefty Nikon for a group photo and the group strips off their green vests and melts into the crowd, leaving a couple of sniggering onlookers and half a dozen bags of meticulously collected detritus.

Click here for a slideshow of Thomas White's pictures from the clean up.