A FLASH MOB is a large group of people who assemble suddenly in a public place, perform an unusual action for a brief time, then quickly disperse. The term FLASH MOB is generally applied only to gatherings organized via social media or viral emails , rather than those organized by public relations firms or for a publicity stunt.
And here is another one also in London: http://www.youtube.com/watch?v=VQ3d3KigPQM
But you can find them all over the world like this one in Antwerp, Belgium: http://www.youtube.com/watch?v=7EYAUazLI9k
Worldwide Pillow Fight Day (or International Pillow Fight Day) was a pillow fight FLASH MOB that took place on March 22, 2008. Over 25 cities around the globe participated in the first "international FLASH MOB", which was the world's largest FLASH MOB to date. On 4th April this year, approximately 200 people went to Largo do Machado for a pillow fight.
You can check the You Tube for more FLASH MOBS.
Now, would you like to take part in a pillow fight?