A vote on a third Heathrow runway will take place later today, and transport secretary Chris Grayling has made a plea for cross-party unity.
Boris Johnson, a long-term critic of a third runway, was challenged on Sunday by a Tory colleague to "put his money where his mouth is" and resign as Foreign Secretary over his opposition to the scheme.
Johnson once said he’d lie down in front of bulldozers to prevent the £14 billion expansion.
He is currently abroad but the government has not revealed his whereabouts for security reasons.
Senior backbencher Sarah Wollaston said that Theresa May's decision to allow him to avoid her three-line whip in support of the Heathrow plan "won't wash" and called on him to make a "principled decision" to stand down.
114,000 extra jobs
Over 40 Labour members said they would go against party policy and support the Government's decision.
Labour is officially opposed to the expansion but Jeremy Corbyn has allowed MPs a free vote on a measure that is supported by trade unions but opposed by the shadow chancellor John McDonnell.
Grayling said yesterday that "thousands of new jobs and the country's ability to compete on an international stage and win new global trade" were at stake.
He said: "I hope colleagues from across the House will now put aside party and political differences to take a decision in the long-term national interest."
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 won’t come at the taxpayer’s expense, Grayling pledged.
Friends of the Earth called the plans "morally reprehensible" and would see the enlarged Heathrow emitting as much carbon as the whole of Portugal.
Greater Manchester's Labour mayor Andy Burnham urged the Prime Minister to guarantee funding for transport projects in the north - including rail - saying the Government's "focus has drifted southwards once again".
"It's far more than just a strip of concrete. There are thousands of people being displaced from their homes, and the air and noise impact," said Calum Harvey-Scholes of Vote No Heathrow.
"We're running headlong into an existential threat to Britain and humanity. Aviation is the fastest growing source of carbon emissions. Heathrow is the biggest, most polluting unit in the UK."
Speaking to Julia Hartley-Brewer, he claimed that "climate breakdown kills more than 300,000 people every year". Air quality studies show that pollution levels around Heathrow are consistently above legal limits.
A Pubic Health England report in 2014 said that approximately 29,000 deaths in the UK annually could be blamed on pollution, and said it was 'equivalent to 340,000 life years' rather than pollution being the cause of 300,000 actual deaths.