THE FINAL decision on expanding Gatwick or Heathrow will not be made for another twelve months.

A year-long public consultation will follow a recommendation to be made by a Cabinet sub-committee in the Government next week, with a vote not scheduled until the winter of 2017/18.

Amid heightened speculation that the additional runway will be built at Heathrow, the Prime Minister has said she will suspend normal rules insisting ministers publicly back the government’s line.

In a letter to ministers the Prime Minister Theresa May said that due to some of them having “strongly-held views,” she will allow “certain ministers some flexibility to set out their personal position on the matter.”

Both Foreign Secretary Boris Johnson and Education Secretary Justine Greening - whose London constituencies are immediately impacted by the decision - are both on record as being strongly against Heathrow expansion.

Next week the Economic and Industrial Strategy (Airports) Sub-Committee chaired by Mrs May will meet to consider the Airports Commission’s recommendations.

The Prime Minister explained that the recommendation will be followed by a “full and fair” public consultation before a final decision is made and put to a vote in the House of Commons in the winter of 2017/18.

Under the longstanding convention of collective responsibility government ministers are expected publicly to agree with and defend the government’s policy positions.

But this tradition will be suspended in a limited fashion in this instance.

Mrs May wrote: “Whichever scheme is decided upon, if the decision is contrary to the previous public positions already taken by some colleagues, or directly affects colleagues’ constituencies, you will not be expected publicly to advocate the Government’s collective decision.

“You will also be permitted, as part of the subsequent public debate on the subject, to restate longstanding views that are already a matter of public record and to pass on the views of your constituents if they are directly affected.”

The suspension of collective responsibility will not apply to all ministers and does not extend to campaigning against the Government line or speaking against the Government in the House of Commons. They will not be allowed to criticise the process by which the decision was reached.

A government spokeswoman was unable to say how long the suspension of collective responsibility on the issue would last, or whether Conservative MPs will be given a free vote when the question finally comes before Parliament.

No MPs for London or Sussex constituencies sit on the subcommittee.

Mrs May's letter followed a protracted debate lasting more than an hour at the regular Tuesday morning meeting of her cabinet.

Asked whether the special arrangement represented a bid by Mrs May to avoid resignations, her spokeswoman described it as "a mature, common-sense approach, recognising that this is a decision of strategic and national importance while acknowledging that some colleagues have strongly-held views on the issues and in some cases have constituency interests".