LONDON, England (CNN) -- Environmental campaigners say they have dealt a blow to the proposed expansion of London's Heathrow Airport by buying up land earmarked for the construction of a controversial third runway.
Impressionist Alistair McGowan is among those who bought the land next to Heathrow.
Greenpeace said the purchase of a field next to the airport threw a "massive spanner" into the plans, which were being considered by the UK government on Tuesday morning amid speculation that a decision to authorize the expansion may be delayed.
The group, which says a third runway will create extra pollution and noise and mean the demolition of hundreds of homes, also said it would resist attempts by Heathrow's Spanish-owned operator BAA to compulsorily purchase the site.
Greenpeace said it intended to divide the land into tiny pieces to be owned by supporters around the world in an attempt to slow down the planning process with hundreds of legal challenges. Watch as campaigners buy up land »
Oscar-winning actress Emma Thompson and impressionist Alistair McGowan were among those who said they had bought the land, about the size of a football pitch, from a local landowner. Tell us what you think about airport expansion
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 said it bought the land from under the nose of BAA with an elaborate ruse. "We had to have a cover. We pretended we wanted land to set up a donkey sanctuary," a spokesperson told the Guardian.
The government had been expected to approve the new runway this week, despite more than 40 parliamentarians in the ruling Labour Party joining opposition parties in demanding it be dropped.
But a spokesman for Prime Minister Gordon Brown, who agreed on Monday to meet rebel MPs for more talks, said only that a decision had been promised "in January," according to the Press Association.
London Mayor Boris Johnson, who has pledged to go to court over any decision to authorise the runway, said the "overwhelming majority" of people were against the move on environmental and economic grounds.
But backers, including the Unite and GMB unions, argue the airport's expansion could create 65,000 jobs.
British Airways chief executive Willie Walsh said the project would probably not be completed until about 2019 or 2020, by which time new aircraft would emit 55 percent less carbon dioxide than planes built in 2000.