Update 11.50am: Pressure is growing on Theresa May to publish the Government's latest Brexit analysis after a report that it had concluded Britain would be worse off, whatever deal is struck with Brussels.
As the Prime Minister prepared to fly out on a three-day trade mission to China, opposition MPs said the public were entitled to know the true cost of leaving the EU.
Government sources played down the leak, saying the document was an "early draft" and that "significantly more work" was needed before the analysis was complete.
The people deserve to know what the government think will happen as a result of its decisions, especially on an issue as important as Brexit. They must release the full impact report. @Emmabarnett @bbc5live pic.twitter.com/hsbTqqxEhH— Chuka Umunna (@ChukaUmunna) January 30, 2018
However Labour shadow Brexit minister Matthew Pennycook said: "Labour has made clear since the referendum that Tory ministers cannot withhold vital information from Parliament and the public about the impact of different Brexit scenarios on jobs and the economy.
"Ministers should publish this information immediately and allow for a full debate in Parliament about its implications."
Liberal Democrat spokesman Tom Brake said: "Theresa May has been trying to hide the truth from the public for months but now her mask is slipping.
"The cold hard reality is that these reports reveal nothing we didn't already know. Of course staying in the EU remains our best option, of course Brexit is going to damage the UK."
The analysis, drawn up for the Department for Exiting the EU and seen by the BuzzFeed News website, found economic growth would be lower under a range of potential scenarios.
Even if the UK is able to negotiate a comprehensive free trade agreement, as the Government hopes, 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%.
The leak did nothing to calm the febrile mood within the Conservative Party, amid concerns over Mrs May's leadership and the direction of the Brexit negotiations with Brussels.
Former Cabinet minister Iain Duncan Smith said the leak was "highly suspicious" and previous forecasts about the impact of Brexit had proved to be "completely wrong".
"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.
"But, I would observe that almost every single forecast coming from Government, and most of the international organisations, has been completely wrong.
He told the BBC: "I think we should take this with a pinch of salt."
A Government source said the analysis had studied the impact of a series of "off-the-shelf" agreements but had not considered Mrs May's preferred option of a "bespoke" agreement.
"An early draft of this next stage of analysis has looked at different off-the-shelf arrangements that currently exist as well as other external estimates," the source said.
"It does not, however, set out or measure the details of our desired outcome, a new deep and special partnership with the EU, or predict the conclusions of the negotiations.
"It also contains a significant number of caveats and is hugely dependent on a wide range of assumptions which demonstrate that significantly more work needs to be carried out to make use of this analysis and draw out conclusions."
Leaked Brexit economic impact report attacked as 'highly suspicious' by furious Eurosceptic MPshttps://t.co/YDj1Lp8ga9
Brexit not good. Reform a must. Remain campaign not run well.
BUT: needs must. % figures show 'scares' not BIG. Shows desperate need by those who know better!— Selva Associates Ltd (@SelvaAssocLtd) January 30, 2018
Earlier: Leaked British government report suggests UK worse off in every Brexit scenario
A leaked British government Brexit impact assessment has warned that leaving the EU will adversely hit almost every sector in every UK region.
According to buzzfeed.com the leaked report, obtained exclusively, shows that the impact of Brexit says the UK would be worse off outside the European Union under every scenario modelled.
The site reports that the analysis, entitled “EU Exit Analysis – Cross Whitehall Briefing” looked at the three most likely Brexit scenarios and found that UK growth over the next 15 years would be lower than expected by a rate of 2-15%.
buzzfeed.com go on to list the following main fundings.
• Almost every sector of the economy would be negatively impacted with chemicals, clothing, manufacturing, food and drink, and cars and retail hardest hit with only the agriculture sector unaffected.
• The North East, West Midlands and Northern Ireland face the biggest falls in economic performance.
• London’s status as a financial centre could be severely eroded.
On the plus side the analysis suggests a trade deal with the US would benefit GDP by about 0.2% in the long term and deals with other non-EU countries and blocs would add a further 0.1% to 0.4% to GDP over the long term.
More as we get it ...