Theresa May has sought to play down the leak of the Government's latest Brexit analysis, after a study concluded Britain would be worse off, whatever deal is struck with Brussels.
The Prime Minister told the weekly meeting of Cabinet that the paper represented "initial work" by officials which had not been signed off by ministers.
She said the document had not looked at the impact on the economy if the Government achieves the sort of "bespoke" trading agreement with the EU it is seeking.
The leak of the economic impact analysis, which was drawn up for the Department for Exiting the EU, triggered renewed demands from opposition parties to release the full details.
The document, seen by the BuzzFeed News website, 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 estimates 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%.
However, Mrs May stressed that the document had only considered a range of "off-the-shelf" arrangements rather than the specific deal the Government is seeking to negotiate.
A No 10 spokesman said: "At the beginning of Cabinet, the Prime Minister noted media coverage of a report purporting to show the impact of Britain leaving EU.
"The PM said this was initial work, not approved by ministers which only considers off-the-shelf scenarios.
"No analysis was made of the bespoke agreement we seek as a matter of Government policy."
But as the Prime Minister headed off for a three-day trade mission to China, opposition parties said the public were entitled to know the true cost of leaving the EU.
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 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 document was an "early draft" which needed further work before it was ready to go to ministers.
"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," the source said.