Sir Sadiq Khan has refused to rule out using taxpayers’ money to fight the Heathrow expansion. Chancellor Rachel Reeves has given her support for a third runway at the London airport.

But the Labour Mayor of the capital, a longstanding opponent of the proposals, signalled he could pursue legal action due to the impact on the environment. Asked if he was prepared to use Londoners’ money, Sir Sadiq told BBC Radio 4’s Today programme: “Look, I’m a pro-business, pro-growth mayor. We recently announced a London Growth Plan because I really believe in the importance of growing the economy.”

Pressed on if he would launch a legal challenge, he added: “I agree with nearly all of Rachel’s policies relating to growth.

“But let’s wait and see what plans Heathrow publish. Look, if Heathrow doesn’t address the concerns I’ve highlighted, then, of course, my job is to stand for London.”

Asked if he would use the mayoral budget, he vowed to “use all the tools in my toolkit if I think it’s wrong in terms of Londoners’ interest, and indeed the national interest”.

Sir Sadiq spoke out against a third runway at Heathrow after Ms Reeves gave her backing in a bid to boost economic growth in a major speech in January.

He said at the time: “I remain opposed to a new runway at Heathrow because of the severe impact it will have on noise, air pollution and meeting our climate change targets.

“I will scrutinise carefully any new proposals that now come forward from Heathrow, including the impact it will have on people living in the area and the huge knock-on effects for our transport infrastructure.”

Prime Minister Sir Keir Starmer and five other Cabinet members, including Energy Secretary Ed Miliband, voted against a third Heathrow runway in the Commons in 2018.