Boris Johnson has faced calls to resign after jetting off to Afghanistan to dodge a crucial vote on approving a third runway at Heathrow Airport.
Images of the foreign secretary meeting his counterpart in Kabul emerged on social media after hours of speculation about his whereabouts, as the government refused to disclose his location for security reasons.
In chaotic scenes, the Foreign Office did not officially confirm what appeared to be a hastily-arranged diplomatic trip until more than two hours after the Afghan ministry of foreign affairs had posted pictures of Mr Johnson with deputy foreign minister Hekmat Karzai on social media.
Mr Johnson, who once said he would lie down in front of bulldozers to stop the project, opted to be out of the country for the crunch vote as Conservative MPs faced a strict three-line whip to back the plans.
However senior Tories urged him to “put his money where his mouth is” and quit – as he would have been forced to resign from the government if he wanted to vote against the Heathrow expansion plan.
Mr Johnson was also mocked by Labour, with fellow London MP Wes Streeting claiming: "Boris Johnson has decided he’s safer in Afghanistan than facing west London Tories."
The overseas trip came as MPs prepared for a late-night vote on the divisive project, which could create thousands of new jobs and capacity, but critics oppose over environmental, noise and financial concerns.
Mr Johnson famously told anti-expansion protestors that he would "lie down ... in front of bulldozers" to prevent a new runway being built, as his Uxbridge and South Ruislip constituency lies under the flight path.
But under collective responsibility, cabinet ministers must vote with the government on key issues – meaning he would have to resign if he wanted to oppose the project.
His actions stood in contrast to international trade minister Greg Hands, who stood down from his ministerial post last week so he could vote against the third runway, despite reportedly being offered the chance to miss the vote by going overseas on official business.
Mr Hands took a swipe at his Tory colleague, telling MPs: "This is not just, for me, a debate about Heathrow, important though that is.
"It's also a debate about being true to your word and to your election pledges."
Prominent Conservative backbencher Sarah Wollaston said Mr Johnson should have resigned "on a point of principle" and it would be an opportunity to "put his money where his mouth is".
"Just being conveniently out of the country, I'm afraid, won't wash," she told BBC Radio 4's Westminster Hour.
Former Tory cabinet minister Justine Greening also took aim at Mr Johnson, tweeting: "Great you're back Greg [Hands]!
"I wouldn't want any long-term MP campaigners against Heathrow expansion to miss their chance to represent their community. #commitment #bulldozer."
Conservative MP Robert Halfon also backed calls for Mr Johnson to resign from government.
He said: “Yes, I think that would be a good thing. I think he’d be quite respected by the constituents but individual MPs will make that judgment."
Jeremy Corbyn, the Labour leader, said: "I would have thought, if nothing else, as a constituency MP he would want to be in the Commons because, after all, his constituency is very, very near to Heathrow, and he has in the past made very strong statements against Heathrow, and, indeed, once he promised to lie down in front of a bulldozer on it.
"If he is unable to be present, then we have to ask the question, 'what on Earth is he doing and who is he representing?
"And his chaos and confusion surrounding the EU negotiations and constant differences of opinion with the government, you really ask the question, why is he still there?"
Shadow foreign secretary Emily Thornberry said: “Boris Johnson likes to call other politicians invertebrate jellies, yet his decision to flee the country rather than make good his previous promises on Heathrow shows him to be the most spineless of all.
“On this issue, he has proven himself utterly devoid of courage, strength, or principle.”
Mick Rix, national officer of the GMB union, which supports the bid, said: "Boris Johnson presumably thinks he's going to get a better reception in Kabul than he would in Westminster today.
"As the foreign secretary flees the country, having abused British industry and broken yet another promise, this time on Heathrow, we're standing up for quality, skilled jobs and backing expansion today."
However Mr Johnson hit back at his critics, saying he had been urged by local councillors to carry on in office so that he could continue to fight the project from within Theresa May's top team.
"Some of my critics have suggested that I should resign over the issue. No doubt they have my best interests at heart,” he said in an open letter to his constituents.
"But it is clear from what is likely to be a large majority of MPs who are in favour of a third runway that my resignation would have achieved absolutely nothing."
The "considerable difficulties" facing the project mean it could be a long time before a third runway is ever built, he said.
Mr Johnson discussed the peace process, countering extremism and girls education on his visit to Kabul, where he met with president Ashraf Ghani, chief executive Abdullah Abdullah, and Mr Karzai.
He said in a statement: "At this important moment when Afghan-led efforts towards peace and a political settlement have gained considerable impetus, I was proud and inspired to be in Kabul to see how the UK is working in support of the Afghan government to achieve this goal."
There was no mention of Heathrow in his comments.
Ms May originally said that ministers with long-standing objections to the Heathrow expansion would be allowed to continue to oppose it at a local level but would not be permitted to speak out in parliament.
The government won the vote on Monday as Labour allowed its MPs to have free rein, despite saying the third runway plan failed to meet its environmental tests.
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies