The government has decided to sacrifice air quality standards across London in order to allow an extra 60,000 flights per year into Heathrow.

Ministers are planning to ask the European commission for a special deal to exempt the capital from official limits on exposure to air pollutants.

MPs representing constituencies under the Heathrow flight path accused the government of “an enormous betrayal” for allegedly breaking a promise to block Heathrow expansion unless air quality standards were met.

John McDonnell, Labour MP for Hayes and Harlington, said the government’s decision, disclosed in a document obtained by The Sunday Times, was also “a disgraceful act of bad faith”.

He added: “Ministers must have been on their feet about 20 times where they said there will be no expansion of Heathrow unless they can meet the air pollution limits.”

He said next week he and other MPs would demand that ministers should explain themselves in the Commons.

Exposure to nitrogen dioxide (NO2 to respiratory problems and premature death in vulnerable people.

Plans to allow flights to land and take off on the same runway at Heathrow as early as 2010 could lead to an extra 60,000 flights per year.

The extra passenger volumes will also generate additional traffic to and from the airport.

A third runway would generate a further increase in flight numbers and emissions.

Susan Kramer, Liberal Democrat MP for Richmond Park which lies under the Heathrow flight path, said: “Poor air quality hurts our health but it’s the issue that the government never wants to talk about when it comes to Heathrow.

“Now we know why: they have a dirty little secret.”

The European Union air quality directive, which comes into force next month, would require the UK to meet limits on NO2 by 2010, in line with World Health Organisation standards.

The government’s plans to secure a waiver from the rules was disclosed in a presentation given to a conference on air quality earlier this month by an official at the Department for Environment, Food and Rural Affairs.

The civil servant from the department’s air quality unit disclosed that the government is drawing up plans to ask Brussels for formal permission to delay compliance with Europe-wide air quality rules.

An environment department spokesman confirmed that the government was expected to apply for a five-year exemption for NO2 emissions and a year for particulates of less than 10 microns in size.

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