It says if the United Kingdom stays in the customs union and free trade area post Brexit, the north would take a 2.5 per cent hit.
However, if there is a no-deal Brexit, the UK Government's assessment of a 9% drop in GDP is even more severe than the Scottish Government's analysis, released last month, of 8.5%. "And is this too high a price to pay to stop a Tory civil war breaking out?"
In the North East - the worst affected area - a free trade deal would result in an 11% hit to growth, compared with 16% under "no deal", and 3% if the United Kingdom stays in the single market.
An official report into the impact of Brexit on the United Kingdom regions has predicted that Northern Ireland will sustain one of the biggest hits to economic growth after withdrawal from the European Union.
SNP MP Peter Grant said: "The leaked United Kingdom government's internal Brexit analysis makes for utterly grim reading, and Theresa May must now end the shameful secrecy surrounding the United Kingdom government's Brexit plans and publish the papers in full - which we now know will have catastrophic consequences for Scotland and the UK's economy".
Leaked figures show the regional impact of three Brexit scenarios.
"This document does not represent Government policy and does not consider the outcome we are seeking in the negotiations", a spokesman for the Department for Exiting the European Union said in an email to Reuters.
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"We are seeking an unprecedented, comprehensive and ambitious economic partnership - one that works for all parts of the UK".
Sky News and the BBC have both published details from the controversial leaked Brexit impact assessment, and it makes grim reading for every region and country that makes up the UK.
Paul Brannen, Labour MEP for the North East of England, said: "This is the type of news we always feared Brexit would bring".
The study suggests that in three different scenarios - staying in the single market and customs union, negotiating a free trade agreement and leaving the EU with no deal - the United Kingdom economy as a whole would grow more slowly than if it stayed in the EU.
"Options for achieving that should not have been swept off the negotiating table, including being in a customs union with our largest trading partner".
Liberal Democrat MP Tom Brake, the party's Brexit spokesperson, said: "This is a damning outlook for Britain".
"The Government need to start being clear what they are fighting for".