Labour is to seek to force the Government to release its latest assessment of the impact of Brexit on the economy through a binding Commons vote.
In an opposition day debate on Wednesday, the party will use the same archaic parliamentary procedure it adopted last year to force ministers to release Brexit impact papers to a Commons select committee.
The move follows the leak of a study, drawn up for the Department for Exiting the EU, which concluded the UK economy would lose out, whatever Brexit deal the Government struck with the EU.
Theresa May sought to play down the document, telling the weekly meeting of the Cabinet that it represented “initial work” by officials which had not been signed off by ministers.
“People voted to leave the European Union in part to give Parliament control about its own future. That means giving MPs the information they need to scrutinise the Government’s approach to Brexit,” he said.
“Ministers cannot keep side-lining Parliament to hide the deep divisions within their own party.
“They should accept this motion and allow the country to have an informed debate about its relationship with Europe after Brexit.”
Unlike a normal opposition day motion, the vote on the “humble address” will be binding on the Government if it is passed in Wednesday’s debate.
In the Commons on Tuesday, a number of pro-Remain Tories joined opposition MPs in calling for the analysis to be released, suggesting the vote could be close.
Fellow Conservative backbencher Antoinette Sandbach said: “I take exception to being told that it is not in the national interest for me to see a report that allows me to best represent my constituents.”
Tory MP Heidi Allen added: “This is a one-time deal only, and I for one owe it to my constituents to prove to them I have exercised full scrutiny.”
Brexit Minister Steve Baker said MPs would be given the “appropriate analysis” carried out by the Government when they came to vote on a final deal with the EU, but said they could not release such information before it had been completed.
He said a report on the BuzzFeed News website about the leaked study was a “selective interpretation” of a “preliminary analysis”.
“It is an attempt to undermine our exit from the European Union,” he said.
According to the BuzzFeed report, the analysis concluded economic growth would be lower under a range of potential scenarios.
Even if the UK was able to negotiate a comprehensive free trade agreement, it estimated growth would be down 5% over the next 15 years.
That would rise to 8% if Britain left without a deal and was forced to fall back on World Trade Organisation (WTO) rules.
Alternatively, if the UK were to retain access to the single market through membership of the European Economic Area the loss would be just 2%.
No 10 said the analysis had only considered a range of “off-the-shelf” deals and had not covered the “bespoke” agreement which the Government is seeking.
There was anger among pro-Brexit Tories at the way the information leaked out.
Former Cabinet minister Iain Duncan Smith told the BBC: “I think the timing in this is highly suspicious in the sense that suddenly in the midst of all this conversation about the European Union we have a leaked document.
“I think we should take this with a pinch of salt.”