The long-awaited decision on which airport expansion scheme should get the go-ahead is to be finally made.
The government will choose which project to back, ending more than a year of uncertainty since the Davies Commission came out in favour of a third runway at Heathrow.
Other shortlisted options are extending an existing runway at Heathrow or building a second runway at Gatwick.
Prime Minister Theresa May will chair a meeting of the airport sub-committee - made up of key Cabinet ministers including Chancellor Philip Hammond, Business Secretary Greg Clark and Environment Secretary Andrea Leadsom - on Tuesday morning as well as the regular meeting of the Cabinet.
Transport Secretary Chris Grayling will then make a statement to MPs at around 12.30pm announcing the decision.
May has moved to head off possible Cabinet resignations by giving ministers freedom to speak out against the government's decision, with the possibility of Heathrow expansion fiercely opposed by Foreign Secretary Boris Johnson and Education Secretary Justine Greening.
Downing Street said any ministers wanting to voice their opposition to the plans would have to seek permission from the Prime Minister in advance.
Following the announcement, a public consultation will be held on the effects of airport expansion and then a final decision by the government, which will be part of a National Policy Statement on Aviation.
This will be put to MPs for a vote in the winter of 2017/18.
A number of groups have come out in support of Heathrow, including devolved governments, many business leaders and politicians.
But Gatwick insists it is the only project that can be delivered, citing concern about the noise and environmental impact of Heathrow expansion.
Gatwick chairman Sir Roy McNulty issued a last-minute plea to the airport sub-committee, saying that allowing London to have "two world class airports" would send a powerful signal to the world that "Britain is truly open for business."
He claimed that the environmental impacts of expanding the West Sussex airport would be "a fraction of those at Heathrow", adding: "Gatwick represents the best chance of something actually happening. It is the deliverable option."
Anti-expansion groups are gathering in Harmondsworth, near Heathrow, and Crawley, near Gatwick, ahead of the announcement.
Environmentalists concerned about the effect of flying on climate change are holding a demonstration outside the House of Parliament on Tuesday morning.
Labour MP Mary Creagh, chairwoman of the cross-party Environmental Audit Committee, has called for assurances from the government that any new airport capacity will comply with key environmental conditions.
She said: "We will be seeking assurances from the government that the airport's proposals meet strict carbon emissions, air quality and noise standards.
"We have seen some international progress on tackling carbon emissions from aviation recently, but we need a clear plan to reduce emissions from aviation to meet our climate change targets."
The Heathrow expansion option was described as "rubbish" by Johnson's former aviation adviser when he was mayor of London.
Daniel Moylan, who is a consultant for Gatwick Airport, told BBC Radio Four's Today programme: "Well, I've always thought that Heathrow is a rubbish idea, going back the last 15 years.
"The pattern of history we see here is that there's a group of people who keep batting for another runway at Heathrow.
"They keep coming forward with proposals, they always fail. And instead of learning their lessons, they have another go at the brick wall."
John Allan, chairman of London First, told BBC Radio Four's Today programme: "From a UK perspective Heathrow is probably the right answer, but the critical thing is that they make a decision.
"What we want above all is more airport capacity in the South East. The most important thing is to get on with it. Even though it is only a step in the road, it is a very important step in the road."
Greening is expected to give her reaction to the decision in a message to her constituents in Putney, south-west London, a source close to the Education Secretary confirmed.
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