Lawyers acting on behalf of four councils in south west London and Berkshire are preparing to take court action unless a third runway at Heathrow is ruled out.

Harrison Grant Solicitors, working for Hillingdon, Richmond, Wandsworth and Windsor and Maidenhead Councils, has written to Prime Minister David Cameron to set out why he cannot lawfully agree a third runway at Heathrow.

The legal letter highlights “insurmountable environmental problems”, which would make a government decision to support Heathrow expansion “irrational or otherwise unlawful”.

It warns Mr Cameron that the recommendations of the Airports Commission’s, which favoured building a third runway, “were based on a flawed assessment of the impacts on air quality and noise”.

The letter says that the commission’s conclusions on air quality were based on an “error of law”.

Lord True, Leader of Richmond Council, said: “This letter is on behalf of the hundred thousand people who voted ‘no’ in the referendum run by Richmond and Hillingdon and the millions of people across London who have said ‘no’ to any expansion of Heathrow, 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.”

Expansion of Heathrow would result in 200,000 extra low-flying aircraft over London and the home counties each year.

Using the World Health Organisation’s noise impact measure, 766,100 people live within Heathrow’s existing noise footprint, the highest number in Europe.

Councillor Ravi Govindia, Leader of Wandsworth Council, said: “It is 2010 all over again with councils lining up against the same disastrous Heathrow plan.

“What is different this time is that air pollution law is now even stricter and Heathrow’s proposed runway is longer, noisier and would destroy more homes. There is no point going through this all again. A third runway at Heathrow cannot happen.”

Robert Gray, Back Heathrow campaign director, said: “Thousands of taxpayers living in these four boroughs will be furious that councils are spending their money on preparing to sue the government, rather than on providing vital local services.

“Many residents work at Heathrow and local businesses have strong links with the UK’s largest single site employer; they will wonder why taxpayers’ money is being squandered in this way.”