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.

And today hundreds of Britons, of all shapes and sizes, stripped down and kept a straight face as they rode on the underground in their underwear.

This comes ahead of the London underground grinding to a halt during crippling 24 hour strike action, starting this evening, which is set to leave thousands of people stranded during Monday morning rush hour.

Bemused passengers on the tube awkwardly averted their gaze as hundreds of commuters stripped down to their underwear for the bizarre annual tradition.

There are some 9,000-10,000 people who take part each year in the global good-willed stunt.

Londoners wearing coats, hats and scarves on their upper half and nothing but underwear, socks and shoes down below braved the winter weather to take part in the craze.

Confused commuters also saw the pranksters take part in a mannequin challenge on the concourse at Kings's Cross Station in central London.

An open invitation was issued to exhibitionists to join others meeting in central London before they took off their trousers and made their way to the Piccadilly Line and boarded tubes across the capital.

Organiser Ivan Markovic said: 'We have been running it for eight years here.

'We travel the Tube on the first Sunday of the year and just make a scene. We make people smile. We make people laugh and we get some lovely reactions.'