May allows cabinet ministers to express personal views after next week’s decision, signalling it is likely to favour third runway.

Theresa May will allow ministers to express their opposition to airport expansion for a period of time after the decision is made next week, in the strongest signal yet that the government is preparing to back Heathrow’s bid to build a third runway.

Analysis Heathrow third runway: what does the Tory cabinet think?

Where Theresa May’s team stand on the proposed expansion of the west London airport

The prime minister told colleagues at a cabinet meeting on Tuesday that opponents of whatever decision was made would have a set period to speak frankly about their opposition.

Downing Street would not confirm whether that meant ministers would have a free vote in parliament to oppose the decision.

The foreign secretary, Boris Johnson, and the education secretary, Justine Greening, are vocal opponents of Heathrow expansion. Crucially, there are no London MPs on the cabinet subcommittee that will make the decision next week. The other two options under consideration are the extension of an existing runway at Heathrow, or the building of a second runway at Gatwick.

The committee members are: May; the chancellor, Philip Hammond; the business secretary, Greg Clark; the transport secretary, Chris Grayling; the communities secretary, Sajid Javid; the Scottish secretary, David Mundell; the environment secretary, Andrea Leadsom; the chief whip, Gavin Williamson; and the party chair, Patrick McLoughlin.

During cabinet discussions, which lasted more than an hour, May told colleagues she expected any final scheme to be a “boost to business and competitiveness” and that the decision would be taken in the national interest.

Guardian writers examine the pros and cons of a third runway at Heathrow airport from three different perspectives

Her spokeswoman said: “The prime minister wanted to approach this in a mature way, recognising that a number of ministers have long held views on this issue.

And in light of that there would be a certain period of time after the committee had taken its decision where they would be able to express those views and they would not be expected to publicly support the government’s decision.

May was to write to colleagues on Tuesday afternoon to set out the precise details of how the process would work, and the period of time when Tories would be able to speak their mind on the issue.

Downing Street said most cabinet members spoke during the meeting, but there was consensus that a decision needed to be made as soon as possible.

The spokeswoman hinted that ministers would eventually have to accept the government’s decision. The decision will be subject to the ministerial code, in the usual way, including the rules of collective responsibility, but with this special arrangement for a limited time. She would not confirm if the period would cover the timescale for a vote in the Commons.

“Once a decision has been taken, certain ministers who have long-held views or particular constituency interests will have some flexibility to set out their personal position.”

No 10 said it was not the expectation that ministers would be able to actively campaign against the decision that was taken. Johnson has previously vowed to lie down in front of bulldozers if they started work on the third runway.

Of the MPs on the committee, Javid is the only one who has expressed strong public support for Heathrow expansion.

Both May and Hammond have expressed tepid concerns about a third runway in the past, and the local council in May’s Maidenhead constituency is one of those vowing legal action if expansion goes ahead.

In 2008, May said she was concerned that if Heathrow expansion goes ahead the quality of life for her constituents will deteriorate significantly.

However, she has been tight-lipped on the issue since entering the cabinet in 2010.

Hammond, a former transport secretary, has also historically expressed concerns about congestion and pollution from Heathrow, saying the airport should improve rather than expand. However, he is understood to be open to the economic case for expansion.

Asked why there was no London MP on the committee, May’s spokeswoman said: “This is about national infrastructure.

One of the things that came through in the discussion was the importance of this for regions across the UK and making sure that, as we take a national infrastructure decision, we take it on the basis of creating a country that works for everyone.”

Zac Goldsmith, the Conservative MP for Richmond Park and former London mayoral candidate, has said he would resign and trigger a parliamentary byelection if the government approves Heathrow, with his constituency one of the worst affected by the flight path.

Goldsmith, who is popular locally, is considering running in any subsequent byelection, leaving May with a difficult decision over whether to stand a Tory candidate against him, or risk reducing her majority.

The Liberal Democrats, who also oppose Heathrow expansion, are thought to be preparing an all-out assault in an attempt to win the west London seat, which recorded one of the highest remain votes in the EU referendum, though Goldsmith voted to leave.

The shadow transport secretary, Andy McDonald, made it clear that party policy was to support Heathrow expansion, which is overwhelmingly backed by some of the country’s largest trade unions, although the Labour leader, Jeremy Corbyn, and the shadow chancellor, John McDonnell, whose Hayes and Harlington constituency contains Heathrow, are opposed to expansion.

The Liberal Democrat leader, Tim Farron, said: “Suspending collective responsibility to avoid a tricky vote is something that Corbyn does to try and paper over the massive schisms in his party, and now, it seems, the prime minister has taken a leaf out of his book.

“The Conservative party made a ‘no ifs, no buts’ promise to people in west London – waiving collective responsibility to save the hides of a couple of ministers will not fly. People will remember this and hold the Tories to account for their actions.”