Theresa May has given ministers with long-standing objections to Heathrow expansion a licence to restate their views at a local level, but made clear they will not be allowed to campaign nationally against the decision to go ahead with a third runway.
The decision to press ahead with expansion of the airport was announced to the House of Commons by Transport Secretary Chris Grayling, who said that after years of wrangling and delay "the time for action is now".
But the Prime Minister was immediately warned she faces a court battle if MPs approve the decision, including from the local council in her own Maidenhead constituency.
Mrs May, who chaired the Cabinet sub-committee which finally gave the green light to the Heathrow plans on Tuesday morning, said the expansion would "ensure that the UK remains one of the best-connected and most outward-looking countries in the world" after Brexit.
Her decision to offer a partial exemption from the principle of collective ministerial responsibility appears to be tailored specifically for Foreign Secretary Boris Johnson, who was the only minister to take advantage of a similar arrangement in 2016 and repeated his opposition to the third runway in Cabinet on Tuesday.
Tory sources confirmed that MPs would be subject to a three-line whip for the vote.
Rumours are rife that Mr Johnson - who once said he would "lie down in front of bulldozers" to stop the controversial development - may find a way to be away from Westminster when MPs vote on the decision.
Despite the strong opposition of a number of Tory MPs with constituencies around the airport, ministers appeared confident of winning the vote, which must take place by July 11.
Although the Labour leadership reacted cautiously to the announcement, the plan - which is backed by some of the big unions - was welcomed by many of the party's MPs, while it also has the support of the SNP.
A more significant hurdle could come from local councils who are threatening to take the case to the courts unless concerns of residents around the airport were properly addressed.
Simon Dudley, the leader of Windsor and Maidenhead Council, said it was among four authorities considering legal action along with the environmental group Greenpeace.
"Let's be clear here, if it doesn't satisfactorily address concerns, then if MPs vote in favour of adopting this National Policy Statement, that opens up a six-week window to a legal challenge and there will be a legal challenge," he told BBC Radio Berkshire.
In his Commons statement, Mr Grayling was keen to stress that Heathrow expansion would bring benefits across the country, with a boost of up to £74 billion to passengers and to the wider economy.
"The time for action is now. Heathrow is already full and the evidence shows the remaining London airports won't be far behind," he said.
"Despite being the busiest two-runway airport in the world, Heathrow's capacity constraints means that it is falling behind its global competitors, impacting the UK's economy and global trading opportunities."
In a statement released by Downing Street, Mrs May said: "Today's decision to support Heathrow's expansion demonstrates this Government's commitment to deliver the jobs and major infrastructure that this country needs to thrive as we leave the European Union.
"This new runway will give us the tools to ensure that the UK remains one of the best-connected and most outward-looking countries in the world."
Mr Grayling said local communities would receive a £2.6 billion package towards the costs of compensation, noise insulation and improvements to public amenities that was among the "most generous in the world".
He expected to see for the first time a six-and-a-half hour ban on scheduled night flights, and said the scheme would only go ahead if ministers were satisfied it would not impact on the UK's clean air obligations.
Mr Grayling would not be drawn on the whipping arrangements for the Commons vote, although in an apparent reference to Mr Johnson's opposition, he said there had been "almost entirely universal support" for the plan at Cabinet.
Former transport secretary Justine Greening, whose Putney constituency lies under the Heathrow flight path and who also opposes the plan, said she did not expect the vote to be whipped.
"I think the Prime Minister is very clear, this is not a party political issue. These are local MPs who need to represent our local communities," she told the Today programme.
Ministers who want to restate their opposition to the third runway at a local level will be required to write to the PM to ask for a waiver, said Number 10.
"No minister will be permitted to campaign actively against the Government position, nor publicly criticise or call into question the decision-making process itself," said Mrs May's official spokesman.
"Ministers will not be permitted to speak against the Government in the House."
The announcement comes after the independent Airports Commission concluded in 2015 that a new north-west runway for Heathrow was the best option for delivering extra airport capacity - a decision endorsed by ministers in October 2016.