They have staged a mass pillow fight, set off phone ringtones in unison and staged an impromptu opera at Paddington station.

But the latest example of flashmobbing, where strangers gather to do something off-the-wall, was billed as the "world's biggest conga line". Organiser Arren Merdinger hoped hundreds would dance from St Paul's Cathedral, across the Millennium Bridge to Tate Modern.

The New York communications student, 21, here for four months, said: "I was involved in the flashmob event in Liverpool Street where everyone danced to their iPods. I thought it was a great idea so I thought I would arrange one and film it for a university project." She sent emails, posted the event on Myspace.com and distributed flyers on the Tube.

Unfortunately, the result was more flash in the pan than flashmob, with only 35 people turning up. Miss Merdinger said: "I was kind of hoping for a couple of hundred people. I guess this will have to do."

Pharmacy technician Tara Brehaut, 24, said: "I'm disappointed there weren't more people here, not like the thousands at Liverpool Street."

Flashmobbing began in the US in 2003, when 150 people gathered at the Macy's store in Manhattan.