A third runway at Heathrow “will be stopped”, Boris Johnson predicted – as he made clear his continuing opposition the project.

The Foreign Secretary – given “special dispensation” by Theresa May to speak out for a limited period – used a television interview to brand it “undeliverable”.

However, Mr Johnson did not repeat his celebrated pledge to protestors to “lie down with you in front of those bulldozers and stop the building, stop the construction of that third runway”.

Instead, speaking at Heathrow, he insisted: “The day when the bulldozers appear is a long way off, if indeed they ever materialise.

Mr Johnson predicted the proposal would be "snarled up" in legal cases – pointing out Tony Blair’s government approved Heathrow a decade ago – adding: “I think it very likely it will be stopped.

“We have been here before and we are going to see an inevitable fight in the courts and I think the chances of success for the proponents of the third runway are not high.”

Mr Johnson also predicted a third runway at Heathrow would bring inevitable clamour for a fourth, saying: “No other great city would do this to its inhabitants.

“New York is going to be the city of beautiful skyscrapers, Paris the city of lights and London in the future, if we go ahead with this project, will be known as the city of planes.”

"We have been here before and we are going to see an inevitable fight in the courts and I think the chances of success for the proponents of the third runway are not high."

The second high-profile Heathrow opponent in the Cabinet, Education Secretary Justine Greening, issued a statement saying she was “extremely disappointed”.

“I will continue to represent the views of my constituents, not least during the forthcoming public consultation on the draft National Policy Statement,” she wrote.

Because MPs will not vote on the expansion for at least a year, there is no immediate threat of any Cabinet resignations.

In the Commons, Transport Secretary Chris Grayling hinted that Conservative MPs will be given a free vote when the time comes, saying the government “won't force MPs with long-standing principles” into line.

Meanwhile, Labour – which is also badly split on Heathrow – declined to say whether it backed expansion, instead setting four tests for the project.