Groups of Londoners hopped on the Underground on Sunday with one item of clothing noticeably missing.

Those taking part in another No Trousers Tube Ride were spotted baring their legs around the capital.

Bare legs and a straight face were the two requirements for everyone taking part. Credit: Kirsty O’Connor/PA

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 group behind the tradition.

The group's Facebook event page for today's stunt claims more than 200 people took their trousers off for the 2019 ride.

The event lists two simple "requirements for participation" - first, participants must be "willing to take trousers off on the Tube" and must also be "able to keep a straight face about it".

Whole carriages were commandeered by those taking part. Credit: Kirsty O’Connor/PA

The idea is that commuters remove their trousers on public transport and act nonchalantly in order to raise a chuckle from their fellow passengers.

An infamously difficult task among London's usually guarded commuters.

Euston Station was a target for those travelling with no trousers today. Credit: Kirsty O’Connor/PA
The No Trousers Tube Ride participants took on one of London's busiest stations. Credit: Kirsty O’Connor/PA

Thousands showed an interest in attending the London edition of the event on Facebook.

The resulting photographs make for a jarring set of images – with Tube carriages, escalators and platforms dominated by bare legs.