On 10th January, around 100 people braved the cold weather to ride the capital`s underground system in their pants as part of the annual No Trousers Tube Ride: London.
The thrill-seekers made the journey on the Bakerloo Line from Charing Cross to Paddington and back surrounded by bemused commuters who had no idea what was happening.
The group event was a meticulously organised affair, with participants told to meet in front of the two fountains to the left of Nelson`s Column in Trafalgar Square at 3pm sharp.
Organisers then divided people into groups before everyone headed to Charing Cross Tube station.
Once inside, they gathered on the northbound Bakerloo Line platform and got on the front carriage, where they removed their trousers and put them into a bag they had brought with them.
They were instructed to pretend they didn`t know each other and not to talk to other trouserless Tube passengers.
Those taking part were instructed to tell fellow commuters that they had forgotten their trousers and to insist that it was merely a coincidence that others had done the same.
They were also instructed to sit in the car as they normally would, and to do `normal` things such as read a magazine or newspaper.
The two requirements for taking part in the event are a willingness to take your trousers off on the Tube and the ability to keep a straight face about it.
Organisers say the bizarre spectacle is to promote more silliness in the world and give people something to laugh at.
The annual event is becoming more popular - with more than three times as many people taking part in London this year than last year.
The day of trouser-free travel was started by a group called Improv Everywhere in New York in 2002, but it is now a global event.