Supersized Heathrow - with third runway and sixth terminal - will be quieter (if you believe Labour spin)

Unveiling the proposals, Transport Secretary Ruth Kelly claimed noise pollution for local residents would fall - even though the number of flights will rise by half.

But protesters said she was "living in wonderland" and claimed the Government had cynically spun the figures to suit its own ends.

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They said those affected by noise pollution from the airport will actually soar to more than two million.

Under the proposals, a third runway and a sixth terminal will be built by 2020.

The number of flights will rise from 480,000 a year today to 702,000 by 2030.

The number of passengers at Heathrow - already condemned as a disgrace for the length of queues and poor facilities - will rise from 68million to 122million a year.

Despite the huge increase in flights, Miss Kelly said those affected by noise pollution would fall from 274,000 in 2015 to 242,000 in 2020 and 205,000 in 2030.

While some areas would experience greater levels of noise, others would be better off, partly through the development of quieter planes.

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Campaigners, however, criticised the 57-decibel benchmark that the Government uses to measure noise pollution.

The proposals suggest the number of those affected by a noise level of up to 57 decibels would fall slightly from about 258,000 today.

But protesters point out that a recent Government study showed people are significantly annoyed by an average noise level of 50 decibels.

If the benchmark is set at 50 decibels instead, a much larger area is covered, with a population of more than two million.

Edward Lister, the Tory council leader of Wandsworth in South-West London - which the Government claims will not be affected - said Miss Kelly should look again at how to measure noise pollution.

Speaking on behalf of a group of 12 local councils opposed to the plan, he added: "Expanding Heathrow may be good business for airport operator BAA but that's small comfort to the two million people living around the airport who will pay the environmental price."

John Stewart, of the anti-expansion group HACAN, said: "Ruth Kelly is in wonderland if she thinks that all this expansion can take place and noise levels will be lower."

But Miss Kelly insisted it was vital to expand the airport.

"Heathrow supports 170,000 jobs, billions of pounds of British exports and is our main gateway to the global economy," she said.

"But for too long it has operated at nearly full capacity, with relatively minor problems causing severe delays to passengers.

"If nothing changes, Heathrow's status as a world-class airport will be gradually eroded - jobs, will be lost and the economy will suffer."