No Trousers Tube Ride: Passengers strip down to underwear on public transport in 'celebration of silliness'

'The idea behind is simple: Random passengers board a subway car at separate stops in the middle of winter without pants'

Chilly commuters hopped on the London Underground with their legs bared for this year's No Trousers Tube Ride – a once-small scale prank that has swelled into a global tradition.

Hundreds declared they had attended the London edition of the event on Facebook, and the resulting photographs made for a jarring set of images - with Tube carriages, escalators and platforms dominated by bare legs.

Established in the US as the No Pants Subway Ride, the annual event began in New York City in 2002 and has since grown into "an international celebration of silliness" according to Improv Everywhere, the improvised comedy and performing arts group behind the tradition.

A statement on the group’s website said: “The idea behind No Pants is simple: Random passengers board a subway car at separate stops in the middle of winter without pants.

“The participants behave as if they do not know each other, and they all wear winter coats, hats, scarves, and gloves. The only unusual thing is their lack of pants”.

The very first event saw a mere seven people take part for eight stops of New York's subway system.

By 2013, however, it was estimated tens of thousands across 60 cities took part – including 4,000 in the US city alone.

Other pranks put on by the group have included a fake U2 concert in 2005, and a flashmob-style performance in which 207 people froze in place at New York’s Grand Central station.

Additional reporting by PA