Britain's most senior civil servant has warned ministers not to speak out publicly over proposals to build a third runway at Heathrow, it has been reported.
Sir Jeremy Heywood, the Cabinet Secretary, wrote to ministers in the run-up to the party conference season cautioning them about commenting in public on the issue, according to the BBC.
In his email, Sir Jeremy is said to have told them that while they could repeat statements made before the Airports Commission issued its final report in July, they should refrain from further comment.
His intervention would appear to reflect concerns that remarks by ministers could make the final decision vulnerable to legal challenge.
However, it is reported to have been received with deep irritation by some ministers.
The commission's report - recommending the construction of a third runway - is highly controversial, with a number of ministers strongly opposed to the plan, as is London Mayor Boris Johnson.
The Government has said that it will deliver its formal response to the commission before Christmas.
Home Secretary Theresa May confirmed that ministers were avoiding public comment on the issue.
"This is an important decision and it is right that Cabinet ministers are not speaking about it publicly until the decision is taken," she told BBC Radio 4's Today programme.
"It is absolutely right that Cabinet ministers do not say anything that could prejudice the decision that is taken and lead to judicial review."
However Labour MP Andy Slaughter, whose Hammersmith constituency lies under the Heathrow flight path, said it was "disgraceful" that ministers with constituencies directly affected by the decision were barred from speaking out.
"This is going to be subject, if Heathrow does get approval, to ligation over a number of years anyway. It is going to be judicially reviewed," he told the Today programme.
"Cabinet ministers have been muzzled on this. I think it is disgraceful that they can't speak up on behalf of their constituents.
"There is so much pressure coming from (Chancellor) George Osborne and others within the Government to go for Heathrow. I think that they just want to bulldoze the proposal through."