Protesters have bought land earmarked for a controversial third runway at Heathrow Airport.

Oscar-winning actress Emma Thompson and impressionist Alistair McGowan are among a coalition of celebrities, green campaigners, scientists and politicians who bought the football pitch-sized piece of land from a local landowner for an undisclosed fee.

Environmental campaign group Greenpeace said the move threw a "huge spanner" into the expansion plans and warned the site would become a focus for protesters.

The site is close to the village of Sipson, which would lose hundreds of homes if the expansion of the airport in west London goes ahead.

Greenpeace said it was inviting members of the public to become beneficial owners and pledge to do what they can to defend the land from the Government and BAA, under the campaign banner Airplot.

Ms Thompson said: "I don't understand how any government remotely serious about committing to reversing climate change can even consider these ridiculous plans. It's laughably hypocritical. That's why we've bought a plot on the runway. We'll stop this from happening even if we have to move in and plant vegetables."

Greenpeace campaigners are creating a message in chalk on the land, visible from the air, which will say Our Climate - Our Land.

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