Hundreds of thousands of homes will be exposed to more aircraft noise from planned new flight paths that will allow 60,000 more aircraft a year to use Heathrow’s existing runways.

The flight paths will be phased in, the first as early as next year, and will affect people living up to 30 miles (48km) from the airport.

The Government is expected within the next two weeks to approve plans for a third runway and sixth terminal at Heathrow, to open by 2020. But ministers are also preparing to authorise more intensive use of the airport’s existing runways.

The Times has learnt that this expansion will require a complete redesign of the flight paths of approaching aircraft.

The points at which aircraft turn to enter their final approach, either from the east or west, will be moved eight miles farther from the airport. Aircraft will already be as low as 4,000ft (1,200 metres) when they reach these points.

Longer landing paths are needed to accommodate “mixed mode”, under which the two runways are used for both take-offs and landings. At the moment one runway is used for landings and the other for take-offs, with the roles switched each day at 3pm to give residents half a day’s respite from the worst noise.

Aircraft will take different routes from the holding stacks to the new turning points, meaning there will be winners and losers in terms of noise.

Residents in many parts of inner London will no longer have aircraft passing within earshot, but millions of people in outer London and the Home Counties will either be exposed to aircraft noise for the first time or find many more aircraft flying directly overhead. The main losers will be those living close to the new turning points, which will be over Reading to the west and Dartford and Woolwich to the east.

Noise levels will also increase in Watford, Amersham, Camberley, High Wycombe, Barking, Rainham, Ilford, Leytonstone, Walthamstow, Barnet, Carshalton and Beckenham. People in Hampstead, Highgate, Islington, Hackney, Mile End, Stratford, Harrow, Ruislip and Henley will no longer hear any Heathrow-bound air traffic.

The Government did not make clear in its consultation document on Heathrow expansion, published in November 2007, that so many people would experience a significant change in aircraft noise. It is possible to work out the changes only by comparing two small-scale maps on pages 53 and 78 of the document.

A report mentioned in a footnote contains more details and states that the extra flights would require “major airspace changes”. The report, by National Air Traffic Services, says that the changes to Heathrow’s flight paths would be so extensive that aircraft departing from Gatwick would have to be rerouted.

John Stewart, chairman of ClearSkies, which represents people living under Heathrow flight paths, accused the Government of expanding the airport by by stealth. “The Department for Transport [DfT] has buried the bad news about new flight paths which will disturb millions of people living in outer London and the Home Counties,” he said.

“It would be the biggest change to flight paths since Heathrow opened over 60 years ago, but it is being done by stealth. Most people who will be affected have no idea what is in store for them.

“The DfT continues to sell the introduction of mixed mode as little more than a technical change.”

Martin Salter, Labour MP for Reading West, said: “Mixed mode will have a significant impact on many people who are not exposed to much aircraft noise at present. We need a better Heathrow, not a bigger Heathrow.”

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