Heathrow third runway: Councils in legal threat over plan
Four Tory councils have threatened to sue the government if plans for a third runway at Heathrow Airport go ahead.
Solicitors acting for Wandsworth, Hillingdon, Richmond and Windsor and Maidenhead councils have written to the prime minister saying expansion would be "irrational or otherwise unlawful".
In July, the Airports Commission (AC) said the plan was preferable to expanding Gatwick.
The government has said more work on the environmental impact was needed.
A final decision on the issue is expected in the summer.
In their letter, the councils remind David Cameron that in 2010 he promised to oppose a third runway at Heathrow - "no ifs, no buts".
Solicitors Harrison Grant, who successfully opposed Heathrow expansion in the High Court six years ago, say the AC's assessment is "flawed".
Conclusions on air quality "were based upon an error of law" and the proposals for reducing noise impact rely on "speculative" mitigation measures which "have been wholly rejected by the industry as unworkable", the councils said.
Lord True, leader of Richmond Council, said: "This letter is on behalf of the 100,000 people who voted No in the referendum run by Richmond and Hillingdon.
"We will consider any action, within the law, to fight against expansion at Heathrow. I urge the government - take heed of our letter. Keep your promises. Let's end this now rather than drag it out into the summer."
"Local people have planned their lives" in the expectation that Heathrow would not expand, said Ray Puddifoot, the leader of Hillingdon Council.
"A third runway at Heathrow would still produce unacceptable pollution and noise and cause the destruction of hundreds of homes and business," he said.
Last week, 13 protesters who disrupted flights at Heathrow in protest against a third runway were given suspended sentences.