Pranksters staged a cheeky invasion of London's underground network to take part in No Trousers On The Tube Day.
What began as a madcap idea by a handful of people on New York City's mass transit system in 2002 has grown into an international celebration of silliness.
Now there are around 9,000-10,000 people who take part each year in the global good-willed stunt.
Hundreds of Britons, of all shapes and sizes, stripped down and kept a straight face as they rode on the underground in their underwear.
Confused commuters also saw the pranksters take part in a mannequin challenge on the concourse at Kings's Cross Station in central London.