Figures published by the London Mayor “blow out of the water” Heathrow’s claim that overall noise levels would fall if a third runway was built, campaigners said.

The figures, part of Boris Johnson’s report on the Estuary Airport submitted to the Airport’s Commission last week, showed Heathrow’s claims assumed the new runway would be operating at only one-third capacity.

They also argued that Heathrow was too optimistic about the introduction of quieter aircraft.

The Mayor’s figures, based on a study he commissioned from the Civil Aviation Authority (CAA), showed if a third runway was built more than 1m people would be impacted by noise, up from 725,000 today.

Chairman of Hacan John Stewart said: “These new figures from the CAA 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 CAA study shows that if a third runway was built at Heathrow people would be disturbed in new areas of London and the south-east.

Heathrow said the number of people within its noise contour fell tenfold since the 70s, despite the number of flights doubling.

It said its modelling showed the number of people within the 55 Leq Heathrow noise footprint would be cut by 45 to 48 per cent by 2030, even with a third runway.

A Heathrow spokesman said: “These significant noise reductions are due to quieter aircraft, the third runway being located farther west, steeper landing approaches, and aircraft landing farther along all three runways.

“In its interim report the independent Airports Commission found that it is possible to add flights while continuing to reduce aircraft noise at Heathrow.”