Ministers could be given a free vote on whether to expand Heathrow Airport, an internal Government document has revealed.
The paper, filmed by a passenger on the London Underground, discusses the "potential waiving of collective responsibility" ahead of the forthcoming decision on airport capacity, 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.
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.
"The Government on this issue seems to be in absolute chaos", he said.
"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".