Ministers could be given a free vote on whether to expand Heathrow Airport, an internal Government document has revealed.
The paper, which was filmed by a passenger on the London Underground, discusses the "potential waiving of collective responsibility" ahead of the forthcoming decision on airport capacity.
The long-awaited decision on whether to expand Heathrow or Gatwick is politically highly sensitive for Theresa May due to divisions within the Tory ranks.
Foreign Secretary Boris Johnson campaigned against Heathrow expansion while London mayor, and Putney MP and Education Secretary Justine Greening is also opposed.
Details of the proposal were contained in an email sent to Sue Gray, the director general of the Cabinet Office's propriety and ethics team, Channel 4 News reported.
A Tube commuter spotted the email printout while standing close to the official on a Central Line train.
The passenger captured some of the contents with a smartphone, including a section clearly marked "waiving collective responsibility" and appearing to indicate that one option would be a free vote.
The disclosure is the second embarrassing document leak to hit the Government within days after the Prime Minister's plans for new grammar schools were inadvertently revealed to press photographers in Downing Street.
The email from Sharon Carter to Ms Gray states that lawyers and colleagues in the Cabinet Office's economic and domestic affairs secretariat "are seeking specific input from us on how to handle potential waiving of collective responsibility".
The document suggests that "one route for waiving collective responsibility would be a free..." with the next few words then obscured by the thumb of the woman holding the printout.
The sentence continues"... allowing ministers to speak against the Government's position in the House".
The document goes on to refer to the situation during the coalition government, when the Liberal Democrats and Conservatives held differing positions, and in the run-up to the European Union referendum vote when Cabinet colleagues were in opposing camps.
In July last year the Davies Commission recommended the building of a third runway at Heathrow, but the Department for Transport announced that further investigation into noise, pollution and compensation would be carried out before a decision is made.
David Cameron was expected to indicate which project would get the go-ahead after the EU referendum, but his resignation following the victory for the Brexit campaign meant the decision was left for his successor, Mrs May.
A Government spokesman said: "The Government remains committed to taking a decision on airport expansion and delivering additional runway capacity as planned by 2030. We will set out next steps in due course."
Shadow chancellor John McDonnell, whose Hayes and Harlington constituency would be hit if the Government decided to expand Heathrow, said any proposal for the site would be defeated in the courts because of the environmental concerns.
He told Channel 4 News: "The Government on this issue seems to be in absolute chaos. On free votes, it's usually for major constitutional matters or moral conscience issues or an individual MP will be given a waiver because of their constituency interests.
"I speak as the constituency MP for Heathrow and I would have expected a proper debate and then a vote. To have a free vote in this way means that (for) virtually every major infrastructure people will be demanding a free vote and now, on other issues, why not grammar schools, why not every other major policy issue?"
Liberal Democrat leader Tim Farron said: "The suggestion that there might be a free vote on Heathrow is farcical - this is a huge decision and the Conservative Government has to make a collective decision and take full responsibility.
"If people disagree they can resign.
"Liberal Democrats are the only party consistently opposed to a third runway at Heathrow and we will fight any plans to allow it to be built."