CLEAN : Hundreds take to London tube

The video discusses a flash mob event in London where participants removed their trousers on the tube. Organized through Facebook and flash mob sites, the event aimed to surprise and amuse the public. The concept originated with Improv Everywhere in New York in 2002 and was introduced to the UK in 2010.

How many people participated in the event mentioned in the text?

Describe the event that the group organized in London.

What reactions do the participants aim to evoke in the public?

What is the main purpose of the group Improv Everywhere?

When did Improv Everywhere start their activities in the UK?