The 2012 International Pillow Fight Day in London

Hundreds of people descended on Trafalgar Square this afternoon for the feathery fracas of the 6th International Pillow Fight Day.

Across Asia, Europe and the Americas city squares were covered with down as strangers clutching pillows battled one another as part of the Urban Playground Movement event.

The first International Pillow Fight was in 2008, and organisers Kevin Bracken and Lori Kufner explained their motivation on their website:

"This is a building block of our goal to spread free event culture to every corner of the world" they write.

"Imagine that anywhere on the face of the Earth, there may some day be free, fun, massive public events like pillow fights and interactive art installations on every day of the year.

"Imagine that in the future, we will be united by our drive to live free, fun public lives! That is the era we dream of."

Participants revelled in the sheer fun of recreating childhood pillow battles.

Patricia Robertson‏@wineweaverusa10m tweeted: "Puff of feathers in Trafalgar SQ London, youthful joy of spring and sunshine at last!!

The fights got underway at 3pm, with a claxon announcing the start, and people dressed in pyjamas, dressing gowns and outlandish bedtime get-up turning the square into a melee of swinging pillows.

The organisers take a distinctly DIY approach to organising the events, declaring: "Our advice to anybody who has ever wondered is to never ask permission. This may change in the distant future if we witness some kind of crackdown against free events and interventions, but in the meantime, it is very unlikely that anybody will say yes.

"We must also remind you: the "permit culture" we citizens witness in city halls around the world is perhaps the single largest barrier to experiencing the full richness of public life in the cities we live in. Do not ask for permission, public assembly is a human right."

Money from the £5 'whack n' keep' souvenir pillows was donated to charity, and one of the few rules at the event was not to whack someone who was unarmed with a pillow or taking a picture.