A third runway at Heathrow would expose more than 370,000 extra people to significant levels of aircraft noise, a new report claims.
More than a million people would fall within the airport's noise footprint should a new landing strip get the go-ahead, according to a new report by London mayor Boris Johnson.
The new figure dramatically contradicts Heathrow's claims that nearly 50 per cent fewer residents would be subjected to noise from the airport by 2030, even with a third runway.
The new statistics were published on Friday (May 23) in Mr Johnson's latest submission to the Airports Commission on his case for a Thames Estuary airport.
His report claims the number of people within Heathrow's 55 Lden noise contour would increase from 725,000 at present to 1,097,200 by 2050. It says this is without taking into account the expected population increase during that period.
The areas suffering from a notable increase in noise, according to the report, would include Chiswick, Hammersmith, Chelsea, Pimlico, Kennington, Camberwell, Peckham, New Cross and Deptford.
In contrast, the document claims a new hub airport on the Isle of Grain would expose just 31,500 people to that level of noise.
It said that since the early 1970s, the population within the airport's noise footprint has fallen around tenfold, despite the number of flights doubling.
But anti-Heathrow expansion campaign group HACAN said the mayor's figures 'blow out of the water' Heathrow's claims that noise levels would fall with a third runway.
HACAN chairman John Stewart said: "These new figures from the Civil Aviation Authority blow out of the water Heathrow's claims that a third runway can cut noise levels.
"They could be a game-changer as they show that Heathrow still has not found a way to deal with the politically toxic problem of noise."
The difference in the two sets of figures can be accounted for by the fact Mr Johnson's report uses what it describes as less 'optimistic' predictions about the rate of technological improvement and assumes the new runway will be fully utilised, with 740,000 flights a year, rather than the 570,000 used in Heathrow's modelling.
The Airport's Commission was established in 2012 to examine the need for extra aviation capacity in the UK.
Its three shortlisted options for expansion include two proposals for a third runway at Heathrow and one for a second runway at Gatwick.
Although the Thames Estuary option favoured by Mr Johnson did not make the shortlist, it has not been completely ruled out by the commission, which is due to make its final recommendations in summer 2015.
The Lden noise measure, introduced by the EU in 2006, takes into account noise over a whole year, giving extra weighting to disturbances at night and in the early morning.
The pro-expansion campaign group Back Heathrow, which was set up with funding from the airport, described the Mayor's plans as 'economic vandalism'.
Back Heathrow campaign coordinator Rob Gray said: "The mayor's claims about aircraft noise are outdated and ignore the huge improvements to both shortlisted Heathrow proposals to address this issue.
"Even the most vociferous critics of Heathrow acknowledge that the number of people seriously affected by aircraft noise is five per cent of the mayor's imaginative estimates.
"Today's submission is a last ditch attempt to keep Boris Johnson’s lame duck proposal on the table. The Mayor is attempting to snatch defeat from the jaws of victory by building a new airport which requires Heathrow to close, destroying one of the UK's best economic success stories.
"This would mean the loss of 114,000 local jobs and threaten the livelihoods of more than 250,000 people in the area who depend on the airport. The Mayor's plans would vandalise the economy of west London and the Thames Valley."