Plane Stupid said it would be carrying out more direct action

One man from Plane Stupid chained himself to the front door of operator BAA at the west London airport, while others blocked the stairs.

The group called Heathrow a "climate change criminal" due to emissions.

BAA said the police eventually removed them because employees were unable to get into work.

Plane Stupid said six of its members were arrested. The police have yet to confirm this figure.

'Growing cause of emissions'

The group said the runway will create higher carbon dioxide emissions due to an increase in air traffic.

If BAA's plans for another runway go ahead, up to 700 homes could also be demolished.

Joss Garman, of Plane Stupid, said the protest was "the start of our direct action campaign to stop airport expansion".

"Since Heathrow is now 60, it's time BAA took a health check - or better, early retirement.

"Emissions continue to rise, with aviation now the fastest growing cause of climate change and, like a cancer, Heathrow is swallowing up villages like Sipson - wiping established communities off the map.

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"In 60 years, Heathrow has grown from being a small local airport into a climate change factory.

"BAA's plan to expand the airport further puts them in the premier league of climate change criminals."

A BAA spokesman said the company will not be giving a response to the groups claims.