More than 60,000 extra flights will pass low over London each year under a government plan to suspend air pollution limits to allow Heathrow to expand.

The two existing runways will be used much more intensively, meaning that people living under flight paths will no longer have half a day's respite from aircraft passing overhead.

The plan will result in an additional 25 million journeys by road to and from the airport each year, causing a sharp increase in air pollution from vehicle exhausts. The worst increases in nitrogen dioxide, which causes respiratory illnesses and premature death, will be along the M4 corridor.

At present, one runway is used for landings and the other for take-offs, with their roles switching at 3pm each day. The Government is proposing to abolish “runway alternation” and replace it with “mixed mode”, under which the runways would in effect be treated as separate airports with continual take-offs and landings on each.

The Government is planning to allow the expansion to start in 2010 despite having promised to adhere strictly to European Union limits on air pollution that come into force that year.

The 2003 White Paper on air transport stated: “We are committed to meeting these standards, and it is clear that major new airport development could not proceed if there was evidence that this would likely result in breaches of air quality limits.”

But ministers are now planning to apply to Brussels for a five-year exemption from the EU limits.

The plan is buried in a paragraph on page 88 of the Department for Transport (DfT) report Adding Capacity at Heathrow Airport, which was the subject of a public consultation that closed in February.

The report says that Britain may apply for “a further five years from 2010 for compliance with the NO2 limit values, subject to [European] Commission approval”. But it fails to set out the consequences for the health of people living around the airport.

Ministers are keen to add capacity as soon as possible at Heathrow, which is already close to its planning limit of 480,000 take-offs and landings a year. They claim that there will be more than £5 billion of economic benefits from allowing the number of flights to rise to 540,000 by 2015 on the existing two runways and up to 702,000 after a new runway opens in 2020.

A delegation of leaders of local authorities that represent more than two million residents around Heathrow will travel to Strasbourg next month to ask the Commission to block the Government's plan by refusing to grant a five-year exemption.

Edward Lister, leader of Wandsworth council, said: “The Government has said all along that if it can't meet the new EU air quality targets then expansion cannot go ahead. Now they are trying to move the goalposts.

“We will be telling Stavros Dimas, the European Environment Commissioner, just what UK ministers are up to. The Government is trying to wriggle out of its air quality commitments so it can wave through yet another expansion at Heathrow.”

Darren Johnson, a Green Party member of the London Assembly, said: “Burying this clause deep in the consultation document is a sign that the Government is embarrassed about the way they have neglected the health of Londoners.

“Applying to the EU for a delay in reaching the air quality legal limits will impact on the health of tens of thousands of people. It goes against the whole spirit of consultation to effectively try to hide that fact from the public.”

A DfT spokesman said: “A variety of options on mixed mode were included in the consultation, including the possibility of introducing additional capacity under mixed mode ahead of 2015, and responses are currently being analysed. The department remains committed to meeting its obligations in respect of air quality under the EU directives ... these obligations will come into force by 2010, or 2015 if the UK is granted an extended compliance period.”

The DfT is considering ways of limiting the increase in air pollution, including the imposition of a lower speed limit or a toll on the M4 near Heathrow.

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