Boris Johnson should resign as foreign secretary in order to vote against the expansion of Heathrow, a senior Tory has said.
MPs are expected to give the green light on Monday to building a third runway at the airport.
But Johnson will conveniently be out of the country meaning he will avoid having to choose between his Cabinet job and his longstanding opposition the plan.
Theresa May has already suffered one resignation over the decision to force Tory MPs to back the plan, with Greg Hands quitting as international trade minister to oppose the airport expansion.
Sarah Wollaston, the Tory chair of the Commons health committee, said Johnson should follow Hands.
“I think this would be an opportunity for a colleague like Boris Johnson to actually put his money where his mouth is,” she told BBC Radio 4′s Westminster Hour.
“Just being conveniently out of the country I’m afraid won’t wash.”
She said voters “might expect him to use this as an opportunity and to resign on a point of principle in order to fulfil that election promise”.
Wollaston added: “We’ve seen a series of gaffes from Boris Johnson. I think many of us are wondering why in fact he has been allowed to stay so long.”
Meanwhile, Johnson has been mocked about missing the vote by Hands.
Trade minister Greg Hands resigned from the government over plans to extend Heathrow as his Chelsea and Fulham seat lies under the airport’s flight path, which is heavily affected by noise.
In his election campaign literature, Hands said he was opposed to the expansion of Heathrow “like Boris Johnson”.
On Sunday, Hands used Twitter to fire a shot at Johnson. He wrote: “Great to arrive back in the UK at Luton Airport in time for the match today and to vote against Heathrow expansion tomorrow.
“I wouldn’t want to be abroad for either of those. #commitments.”
May has said the government’s believes to increasing capacity at Heathrow was important for “the ambitions we have as a trading nation for the future”.
And she has defended allowing Johnson to skip the vote. “The foreign secretary early next week will be what I would describe as the living embodiment of global Britain,” she said.
“He will be out there actually showing the UK’s continued presence around the world and the work that the UK continues to do around the world with our diplomacy, working on so many of the issues and challenges that we face across the world today.”
Jeremy Corbyn has decided to allow Labour MPs a free vote on the expansion plans.
His decision follows big pressure from trade unions like Unite and the GMB, who have long campaigned for a third runway as the key to more jobs in construction, travel and retail.
It also means that Shadow Chancellor John McDonnell, whose London constituency is under the Heathrow flight path, can continue his opposition to the third airport.
On Sunday night, Len McCluskey, the head of the Unite union, wrote to all Labour MPs urging them to back the expansion on Monday, saying it was “the opportunity to create hundreds of thousands of new jobs”, putting him at odds with Corbyn.
In a letter seen by the Guardian, he wrote: “We urge you to make the right choice. Your action in the next few days matter to us.”
Meanwhile, more than 40 Labour MPs have said they will disregard their frontbench and support a third runway at Heathrow.
The group whose constituencies span the country put their names to a letter to colleagues in the party urging them to support a project they say could create 180,000 jobs across the UK.
Those who have signed the letter include many critics of the party leadership, including Luciana Berger, John Mann, Mike Gapes and Wes Streeting.
They wrote that supporting the scheme is right “in principle”, saying: “It’ll create up to 180,000 new jobs across the country, delivering growth and connectivity for our constituents.
“As this project will span multiple parliaments – including, we hope, a Labour government – it’s our responsibility to secure strong cross-party backing for this project.”
The MPs disagreed that the expansion plan failed to meet its four tests for support: increased capacity, C02 reduction, minimised noise and shared benefits across the UK, writing: “Monday night’s vote is not a blank cheque – the huge benefits from expansion can only be achieved if Heathrow also meets stringent tests on air quality and noise.
“We will work to ensure legally binding safeguards are in place that will mean a new runway can only be built if it is environmentally sustainable.”
Ahead of the vote, officials said the expansion of Heathrow would create 114,000 extra jobs in the area around the airport by 2030, with an extra 16 million long-haul seats by 2040.
It would represent the first full-length runway in the south east since the Second World War, the Department for Transport said.
Opponents have attacked the scheme on environmental, noise and financial grounds grounds, with Friends of the Earth saying it was “morally reprehensible” and would see the enlarged Heathrow emitting as much carbon as the whole of Portugal.