A coalition of councils has threatened the Prime Minister with legal action should a third runway at Heathrow get the go-ahead.

Hillingdon , Richmond, Wandsworth, and Windsor and Maidenhead Councils have joined forces to appoint the law firm which was behind a successful 2010 High Court challenge against legal expansion.

Harrison Grant Solicitors has written to the prime minister on their behalf explaining how "insurmountable environmental problems" would make government backing for a new runway "irrational or otherwise unlawful".

Its legal missive warns David Cameron that the Airport Commission's recommendation for a third runway was "based on a flawed assessment of the impacts on air quality and noise".

'An abuse of power we are willing to challenge in the courts'

Hillingdon Council leader Ray Puddifoot said: "The Government has made promise after unequivocal promise that this runway will not be built and local people have planned their lives accordingly.

"There is no good reason to change their minds. A third runway at Heathrow would still produce unacceptable pollution and noise and cause the destruction of hundreds of homes and business.

"To go back on the promise would be more than distressing and unfair, it is an abuse of power that we are willing to challenge in the courts."

Harrison Grant's letter states that the commission's conclusions on air quality "were based upon an error of law" and that proposals for reducing noise impacts rely on mitigation measures "which were speculative and have been wholly rejected by the industry as unworkable".

Comedian Alistair McGowan joins protesters outside the High Court ahead of the successful legal challenge in 2010

Air quality conclusions based on 'error of law'

The letter also says Mr Cameron's previous promises not to allow a third runway have created a "legitimate expectation" among those living close to Heathrow that expansion would not be permitted.

And it describes the government's approach to consultation as "selective, inadequate and incomplete".

"In the absence of rational grounds for thwarting and frustrating the prior representations and promises, there is an abuse of power correctable by the courts," it concludes.

Harrison Grant also asserts that the current plans are more damaging than those overturned at the High Court in 2010, as more land is needed, there would be more flights and the extra runway would be longer this time, enabling it to accommodate the largest planes.

The councils behind the threat of legal action say Heathrow expansion would mean an extra 200,000 extra low-flying aircraft over London and the Home Counties each year, and the creation of new flight paths over densely populated areas not previously subjected to aircraft noise.

The Airports Commission recommended last summer that a third runway at Heathrow should be allowed , provided several conditions can be met.

Hammersmith & Fulham and Hounslow councils missing this time

The government announced in December that it was postponing a decision on expansion to allow for a thorough review of the environmental evidence.

It is expected to announce this summer whether it supports a third runway at Heathrow or a second one at Gatwick Airport.

The then Labour government gave the go-ahead for a third runway in 2009, but that was overturned the following year when a High Court judge ruled the consultation process had been invalid.

Six councils were involved in that legal challenge, including Hammersmith & Fulham and Hounslow councils as well as those behind the latest legal warning.

Richmond Council leader Lord Nicholas True 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."

A Department for Transport spokesman said: "We would not comment on speculative legal action.

The government has accepted the case for airport expansion in the south-east and is undertaking a package of further work, including testing the commission’s analysis further against the government's new air quality plan, as recommended by the Environmental Audit Committee.

"We want to see the best possible package of measures to mitigate the impacts on local communities and the environment. We expect to conclude this work by the summer."

A Heathrow spokeswoman said: "Heathrow's new plans for expansion don’t force a choice between the environment and the economy – it will deliver for both.

"The government’s independent Airports Commission confirmed a bigger Heathrow can be a better neighbour. That is because we have changed our plan completely to meet the tests the Prime Minister himself set – fewer people impacted by aircraft noise, offering more predictable respite than we can now, and meeting environmental and air quality limits.

"That is why in over three-quarters of our local communities, more people support expansion than oppose it."