Crowds met outside the National Gallery in the city's Trafalgar Square for the 10th annual No Trousers Tube Ride before heading underground where they boarded trains on different Tube lines across the capital.

More than 100 people piled on to the Piccadilly Line, where they struggled to remove their trousers due to the large crowds.

Regular Sunday passengers were left bewildered as men and women sat in their brightly-coloured underwear talking or reading, or taking pictures of each other.

After changing to the Jubilee Line at Green Park, the group got off at Canary Wharf to do some aerobics on the platform before jumping on another train.

Other groups set off for London landmarks, including one heading to parliament.

Sisters Tessa and Matilda Deterding said they had come for the first time because they liked the idea behind it.

Tessa, 24, from London, said: "We read about it and thought it sounded hilarious. I wasn't nervous about it.

"I quite like the sentiment behind it, instead of a stiff upper lip it's having a bit of a laugh."

Matilda, 22, added: "I did especially pick out my pants, you have got to pick out a nice opaque one. You don't want to give too much of a spectacle."

The event is part of the worldwide No Pants Subway Ride, which began in New York in 2002 and has since spread to over 60 cities around the globe including Tokyo, Jerusalem and Moscow.

The London event was organised by the Stiff Upper Lip Society, which asked participants to "avoid thongs/budgie-smugglers/anything see-through though, as we aim to amuse, not offend, fellow Underground users".

One of the organisers, Farhan Rasheed, said there was not really an aim to the event, it was just a bit of fun.

Australian Associated Press