An official report into the impact of Brexit on the UK regions has predicted that Northern Ireland will sustain one of the biggest hits to economic growth after withdrawal from the European Union.
Brexit impact studies released to MPs by the Government reveal the North East of England and West Midlands will be worst hit.
London will take the least damage, according to the controversial forecasts which ministers were forced to release after they were leaked to the media and amid pressure from Labour and pro-EU Tories.
MPs have been reading the documents, which were prepared by the Department for Exiting the EU, under controlled conditions, but the figures have been leaked.
They are likely to be seized upon by backers of a "soft" Brexit to protect the economy, as Theresa May holds crunch meetings of her inner "war Cabinet" of senior ministers today to thrash out what kind of trade relationship the UK will seek in negotiations.
The figures showed that Northern Ireland would take an 8% hit to economic growth under the Government's preferred outcome of a free trade deal with the EU, while leaving with no deal will result in a 12% dip, and staying in the single market amounts to a 2.5% decline. The North East would take an 11% hit to economic growth under the Government's preferred outcome of a free trade deal with the EU, while leaving with no deal will result in a 16% dip, and staying in the single market amounts to a 3% decline.
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 UK stays in the single market.
By comparison, London would sustain just a 2% hit to growth if the UK gets a free trade deal, 3.5% in a no deal scenario, and just 1% if the country stays in the single market.
Leading local economist John Simpson said the figures were "no surprise".
"They are of an order of magnitude of the long-term consequences of Brexit we have been forecasting," he said. "This is a moment when the economics of Brexit are being appreciated. The politics of simply taking back control, and being counterbalanced by economic problems.
"Northern Ireland is vulnerable in Brexit talks and that is now being recognised on a professional basis."
Sinn Fein MP Chris Hazzard has said the Conservatives must not be allowed to inflict profound economic damage on the north of Ireland. "This staggering British Government leak confirms what many across society have been saying since, and before, the Brexit vote - dragging the north from the EU has the potential to devastate our local economy," he said.
"The potential of a 12% downturn in the northern economy comes following a decade of Tory policy designed to starve our economy of resources.
"The impact on infrastructure, on public services, on workers and business owners will be profound.
"With each passing day, and with each British Government Brexit blunder, the case for designated special status continues to strengthen."
Alliance deputy leader Stephen Farry MLA said the stark figures should be a "reality check" for the Government.
"It is important to remember Northern Ireland is already starting in a worse economic position than other regions due to our legacy of division and violence," he said. "These figures also do not take into account the impact of a hard border and the wider impact on the Good Friday Agreement and the fabric of Northern Ireland society.
"This should be taken as a major reality check for the UK Government.
"The sobering evidence is one of drastic consequences for the UK as a whole, but in particular for the most disadvantaged regions.
"It shows the risks the Government are taking through their current brinkmanship and allowing hardline Brexiteers in the Conservative Party and DUP to set the agenda."
Liberal Democrat Brexit spokesman Tom Brake said: "This is a damning outlook for Britain. The Tories are putting everything on the line because they do not care about the lives and livelihoods of the people of the UK. The Government need to start being clear what they are fighting for. They are still keeping no deal on the table despite how crippling it would be to the regional economy."