Chris Grayling is to confirm the government’s final plans for a third runway at Heathrow as the Tories prepare to impose a three-line whip in favour and Labour considers whether to remove its backing for the project.
The transport secretary will set out his proposals for the expansion to senior colleagues on the cabinet’s economic subcommittee on Tuesday morning, before the decision goes to the full cabinet for approval.
He is then expected to make a statement to MPs, during which he will warn that there is no alternative option if they block the third runway, as he outlines the national policy statement detailing the noise, air quality and cost requirements.
The Guardian understands the government is considering whipping its MPs on the vote, which will follow within 21 sitting days of parliament, although Whitehall insiders suggested it would be sooner to avoid any rebellion gathering momentum.
Grayling is believed to be among those in favour of a three-line whip, although the government has also come under pressure from senior figures, such as former transport secretary Justine Greening, to offer a free vote. One government insider said: “There has never been a free vote on a manifesto issue.”
Downing Street is understood to be considering allowing MPs with constituency interests to dissent locally, while vocal opponents such as Boris Johnson and the international trade minister, Greg Hands, could be permitted to miss the vote by being out of the country on official business.
However, one source close to the foreign secretary, whose west London seat would be affected by the airport expansion, insisted Johnson’s opposition had not waned, while another said he wanted the chance to vote against.
Greening, a leading critic of the third runway who is lobbying No 10 and the whips for a free vote, told the Guardian: “This is not a party political issue and MPs should be able to represent their local communities in the Heathrowvote.”
She also raised concerns over the costs of the scheme, which critics said could cost up to £15bn in new rail links. “I think a lot of MPs who are representing northern seats are also increasingly concerned about the sheer amount of tax-payers’ money that this as a project is going to consume,” she said.
About 30 Tory MPs oppose the government’s plans, which are broadly supported by the Democratic Unionist party, the Scottish National party and scores of Labour MPs. However, Heathrow critics believe that a number of SNP and DUP MPs could be persuaded to vote against.
The Tory MP Zac Goldsmith, who forced a byelection over his party’s support for expansion and has said he will vote against, told the Guardian: “The odds have always been in Heathrow’s favour because they have unprecedented, unhealthy access to government. But they’re weaker now than they have ever been.
“Members of the SNP and DUP are openly questioning the promises made to them by Heathrow about connectivity, numerous Conservatives will vote against expansion, and if Labour come out against, I don’t think the government can get it through.”
A Heathrow spokesman said: “The government is best-placed to comment on their timetables. What is clear is that the case for expanding Heathrow has never been stronger.
“We’re looking forward to the promised parliamentary vote on the final national policy statement before the summer recess enabling us to get on with delivering this critical project.”
Labour fought the most recent election on a manifesto that suggested the airport’s third runway would have to satisfy four tests relating to noise, air quality, climate change and economic growth.
The shadow chancellor, John McDonnell, a close ally of Jeremy Corbyn and a longstanding opponent of a third runway, has said he could not see any way Heathrow could meet the tests.
A senior Labour source said the party had always made it clear its support for a third runway was conditional on the tests being met.
A second party insider said: “Grayling really needs to be able to demonstrate some significant improvements on what has so far been proposed. One of the problems is that he is is going to be looking for parliament, including the opposition, to put some faith in him to deliver. I don’t think that there’s that many MPs that have that.
“We recognise that there are capacity demands at the moment and if this plan falls through then of course we’d have to look at alternative proposals. It’s back to the drawing board.”
However, Labour’s largest union backer, Unite, is a firm supporter of the third runway and the benefits it would bring in terms of jobs, economic growth and increased capacity.
A Unite insider said: “You won’t address these issues by kicking it into the long grass.”
A Whitehall source said: “The idea that you can pick some other option at this stage shows the lack of understanding in the process. When the government decided on this as its preferred scheme, all other options fell away.
“The Labour party may not like the idea but they need to know that if they vote this down, it’s no new airport capacity in the south-east for at least 10 years. That’s not a good idea when after Brexit we need to be a global trading nation.”