Emma Thompson and Alastair McGowan among those who have bought one-acre plot right at heart of proposed development

Land earmarked by Heathrow owner BAA to build a third runway has been bought by a group of celebrities, scientists, politicians and green campaigners in an attempt to severely delay the development. The new runway would make Heathrow Britain's biggest single source of greenhouse gas emissions.

Oscar-winning actor Emma Thompson and comedian Alastair McGowan, along with Conservative party green adviser Zac Goldsmith, Greenpeace director John Sauven and others, have signed the deeds for a one acre field on the edge of the village of Sipson, which will have to be demolished to make way for the runway. The plot lies right at the heart of the proposed runway development.

The new owners said that they intended to divide up the acre plot into small parcels and then sell them, without making a profit, to people concerned about climate change all around the world. As many as 4,000 people could end up owning the scrubland, which lies behind the car park of the William IV pub and next to an old gravel quarry.

The government would use its powers to issue compulsory purchase orders for the plots but lawyers said yesterday that the existence of thousands of owners would make this process time-consuming and expensive. Similar tactics have been used successfully to protect tropical forests.

Transport secretary Geoff Hoon is expected to give the green light to a third runway and a sixth terminal at Heathrow when the decision is announced. Yesterday business and aviation groups called for the runway to go ahead in newspaper advertisements, arguing it was vital for jobs, economic growth, investment and the long-term competitiveness of the UK's economy. Colin Matthews, BAA chief executive, said: "A third runway will only go ahead if strict environmental limits are met."

Emma 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."

Others sharing the ownership of the plot were named yesterday as Labour MP John McDonnell, Conservative front bench transport spokeswoman Justine Greening, Lib Dem MP Susan Kramer and climate scientist Dr Simon Lewis.

"It's a very good time to enter the property market. If BAA want my patch they will have to negotiate with me – and why would I want to sell it to them?" said Kramer.

McGowan said: "The government is sticking two fingers up to the environment and the people of this world. By giving this runway the go-ahead Gordon Brown is effectively holding a giant blow torch to the polar ice-caps and saying 'Melt, Melt !'"

No details have been given of the price paid to the local landowner, or what individuals will be asked to pay. "No profit will be made", said Greenpeace director John Sauven. "This is public activism. We will resist all attempts at compulsory purchase and will represent millions of people from across the world at any planning inquiry."

At full capacity, an expanded Heathrow would become the biggest single source of C02 emissions in the country. It would emit nearly 27m tonnes of CO2 every year – equivalent to the emissions of 57 of the least polluting countries in the world combined.

Yesterday, Greenpeace said that it took them nearly a year to identify the land and buy it from under the nose of BAA. "We had to have a cover. We pretended we wanted land to set up a donkey sanctuary."

Linda McCutcheon, chair of No Third Runway Action Group and a Sipson resident said that she thought the new owners would not have paid much more than the cost of agricultural land – about £3,500 an acre. However, similar land, also without planning permission, in Middlesex is on the market for more than £100,000 an acre.