The Royal Borough will be involved in the appeal granted to a coalition of councils and environmental groups opposed to Heathrow's third runway.
Council leader Simon Dudley (Con, Riverside) has confirmed this afternoon that the borough will be part of the appeal granted after the third runway opponents lost a bid for a judicial review into the Government's support for the airport's expansion in May.
It follows a vote taken last month in which councillors overwhelmingly backed the council's participation in legal action if the appeal was granted. It is set to start on October 21 after being given the go-ahead by the Court of Appeal.
Cllr Dudley said: "The judge feels there are definitely some questions to be answered around all of this."
But he added: "I would not say I am confident (the appeal will work)."
The election of Heathrow expansion critic Boris Johnson - who Cllr Dudley backed - as Tory leader and, as of tomorrow, Prime Minister, is of interest to the council leader, but he stopped short of expecting Mr Johnson to reverse the Government support for the new runway.
"He has said he will follow the legal action with interest," Cllr Dudley said.
"I think something else that will be interesting will be who he appoints Secretary of State for Transport.
"That may give an indication about his view on transport issues."
The judicial review was quashed by High Court judges in May after the Royal Borough joined forces with Wandsworth, Richmond, Hillingdon and Hammersmith and Fulham councils, Greenpeace and the Mayor of London to challenge the Government's support for a third runway.
Their challenge revolved around climate change, air quality, noise and surface access.