Green groups prepare for battle as government plans for a third runway at Heathrow airport come to light.

Environmentalists have pledged to stop the construction of a third Heathrow runway planned by the government. Campaigners say that thousands would have to leave their homes if construction went ahead.

It was thought that the threat of air pollution would prevent another runway from being built but The Observer has revealed that the government is keen to increase the size of Britain's biggest airport.

In his pre-budget report Gordon Brown said that the government was planning a new study aimed at 'identifying solutions that would allow' the runway to be built.

John McDonnell, the Labour MP for the Hayes and Harlington near Heathrow, said that the government was determined to build a third runway.

He met the aviation minister Karen Buck before Christmas according to The Observer. He said: “The industry and government are doing everything they possibly can by way of trying to create an atmosphere of inevitability about Heathrow.” McDonnell said that cross-party opposition around Heathrow would vehemently oppose any construction.

In the pre-budget report Gordon Brown remarked on the importance of Heathrow’s role in supporting economic growth. He laid out plans for extensive modeling work to “understand the nature and extent” of air quality issues at Heathrow.

The report said: “The work is aimed at identifying solutions that would allow construction of a third runway to take place within relevant air quality limits.”