The Government wants to sacrifice air quality across London to allow an extra 60,000 flights a year into Heathrow, according to reports.
The Sunday Times says ministers plan to ask the European commission for a special deal to exempt the capital from official air pollutants limits.
Flight path MPs say the move is 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 newspaper was an act of bad faith.
Mr McDonnell said he and other MPs would be demanding minister explain in the House of Commons next week.
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