A new consultation on plans for a third runway at Heathrow as been branded as illegal because of bias by ministers towards the expansion, councils near the airport claim.
Four Conservative-run councils have said that “a consultation, to be lawful, must be approached with an open mind”.
The intervention threatens to prolong uncertainty over the future of the west-London hub, The Times reported on Saturday.
The Royal Borough of Windsor and Maidenhead and the London boroughs of Hillingdon, Richmond upon Thames and Wandsworth contend that pro-Heathrow statements made by Conservative ministers including transport secretary Chris Grayling could mean that it is unlawful.
Expansion at the airport has been under discussion for more than a decade. The plan was shelved when David Cameron became prime minister in 2010.
He subsequently set up a commission under the leadership of Sir Howard Davies to study airport expansion in the south-east.
The Airports Commission concluded in July 2015 that a third runway at Heathrow was the best solution to deal with congestion at airports around London.
Having accepted but not implemented Sir Howard’s report, the government re-opened the debate with another consultation in October to take into account the latest noise analysis and evidence on the impact on air quality of expanding Heathrow capacity from 80 million passengers a year to 140 million.
Responses to the consultation had to be in by before Christmas. The boroughs questioned the legality of the inquiry in their responses.
Their submissions cite pro-Heathrow comments from Grayling and former aviation minister Lord Callanan.
The transport secretary said in October that the government was “aiming to give [the third runway] the formal go-ahead in the first half of next year” and that the expansion would “make a difference right across this country”.
The four boroughs are all members of the No 3rd Runway Coalition, which has long argued that expansion should be stopped because of noise and air pollution. Labour signalled over the summer that it could try to block a new runway on the same grounds.
Coalition chairman Paul McGuinness said: “There’s a growing sense that the case for Heathrow’s third runway is falling apart.
“The evidence, including the government’s own, simply no longer stacks up to support it. The only thing they seem to have on their side is the [Department for Transport], whose prejudgment in advance of its own consultation is now raising serious legal questions in the year ahead.”
A Department for Transport spokesman said: “We have been clear that our preferred option for increasing airport capacity is a third runway at Heathrow.
“We have consulted with an open mind and once we have reviewed all of the submissions we will set out how we intend to proceed.”