Alistair McGowan says he plans to fight the expansion plans all the way
Land earmarked for the construction of Heathrow's third runway has been bought by anti-expansion protesters.
Land the size of half a football pitch near Sipson village - which would lose hundreds of homes in the expansion - was bought by a Greenpeace coalition.
It has pledged not to sell the land to the government or BAA if the airport expansion gets the go-ahead.
Greenpeace director John Sauven said: "We've thrown a massive spanner in the engine driving Heathrow expansion."
Four key Greenpeace campaigners - including actress Emma Thompson and impressionist Alistair McGowan - bought the land for an undisclosed fee.
Tory front bench spokeswoman Justine Greening and Lib Dem MP Susan Kramer were given a piece of the title to the land by Greenpeace and the group hopes to hand more of the land parcel to others in a bid to complicate any attempt to force them to sell.
We'll stop this from happening even if we have to move in and plant vegetables
They have said plans to increase flights at the airport from 480,000 to 720,000 would create unacceptable noise and pollution.
But BBC transport correspondent Tom Symonds said recent planning legislation included clauses that allowed the courts to consider whether or not a land purchase that blocked planned development was "vexatious or frivolous".
This could, in turn, scupper Greenpeace's plans to obstruct the construction for years.
Our correspondent said the government was due to rule on the plans as early as this week, but that decision may be further delayed.
The airport industry, business and union leaders have said Heathrow's expansion is vital for the British economy's long-term competitiveness and supporters have suggested work on the runway could create up to 65,000 jobs.
Ms Thompson said: "I don't understand how any government remotely serious about committing to reversing climate change can even consider these ridiculous plans."
Mr McGowan said he is in the fight for the long term.
"If it gets to the bulldozer stage, we'll be here getting in the way."
Protesters, including Mr McGowan, have written the words "our climate - our land" on the plot.
Mr Sauven said the group of new landowners would challenge any attempt by the government to force them to sell: "As the new owners of the land where the government wants to build the runway, we'll resist all attempts at compulsory purchase.
"The legal owners of the site will block the runway at every stage through the planning process and in the courts."
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