LONDON - THE British government was to approve on Thursday plans for a third runway at London's Heathrow airport, the world's busiest air hub, despite angry opposition from green groups and locals, reports said.

Mr Geoff Hoon, Transport Secretary in Prime Minister Gordon Brown's government, was to announce the move to the House of Commons, British media reported, citing government sources.

The news has already prompted a furious reaction from campaigners, who have pledged to fight every step of the way to stop it.

They say building a third runway, which would increase the number of flights at Heathrow from around 480,000 to 700,000 a year, would fly in the face of government pledges to tackle climate change through cutting emissions.

'If it's a green light, it will shred the last vestiges of Brown's environmental credibility,' Mr John Sauven, executive director of environmental campaign group Greenpeace.

'An expanded Heathrow would become the single biggest emitter of CO2 (carbon dioxide) in Britain... we'll fight it every step of the way because the lives of millions of people depend on us all slashing carbon emissions.'

Greenpeace is trying to block the nine-billion-pound (S$19.4 billion) project by buying a plot of land in the middle of the proposed runway site.

It has sold miniature parts of the land to around 6,000 Britons opposed to the expansion in a bid to frustrate government efforts to buy it up through compulsory purchase.

Local residents are also opposed to the scheme, saying noise levels from the airport will become unbearable. The scheme would see the village of Sipson and 700 homes bulldozed.

Those in favour of the third runway, including Brown himself and business leaders, say the expansion of congested Heathrow is vital to help London remain a leading business centre.

The project, which would include a sixth terminal and is due to be completed by 2020, will also create around 65,000 jobs at a time when Britain is on the brink of recession.

Employers' organisation the Confederation of British Industry (CBI) says a third runway would generate wider economic benefits of around seven billion pounds per year.

'The case for giving Heathrow the capacity it will need for future growth is very strong, with the future prosperity of London and the wider UK economy depending on it,' it said.

'This is a once in a generation opportunity to ensure that the UK has the infrastructure it requires to play its full part in a global economy.'

Business Secretary Lord Peter Mandelson summed up the government's position late Wednesday, telling the BBC: 'Heathrow's got to have a future - we need it for our economy.

'But we've also got to take into account our climate change ambitions and obligations.'

More than 40 lawmakers from Mr Brown's ruling Labour Party are opposed to the scheme and the main opposition Conservatives, who are ahead in the opinion polls, say they will scrap it if they win the next general election, to be held by mid-2010.

'A third runway at Heathrow would be an environmental disaster and will prove that you cannot trust a word Gordon Brown says on climate change and pollution,' Conservative transport spokesman Theresa Villiers said.

The government is expected to try and limit opposition to the scheme by announcing a package of investment in public transport and strict monitoring of noise and pollution levels.

The Department of Transport declined to comment on the reports that a third runway would get the go-ahead. -- AFP