The frontrunner in the Tory leadership race vowed to his Uxbridge and South Ruislip constituents four years ago he would “lie down with you in front of those bulldozers and stop the building, stop the construction of that third runway".

However, Johnson refused to reassure anti-expansion campaigners earlier this week that he would scrap the scheme if he got into power, and at a hustings organised by the Conservative Party’s 1922 Committee of backbenchers on Wednesday (12 June) he was ambiguous on the matter, according to The Times.

Asked by Greg Hands, a supporter of Jeremy Hunt who resigned from the government to vote against the runway last year, when he would cancel the expansion scheme if he became prime minister, Johnson replied that it had now been approved by parliament.

Johnson was foreign secretary when parliament voted in favour of Heathrow expansion last June.

Campaigners fighting the proposed plans had their High Court challenge against a third runway dismissed last month.