The North East, which overwhelmingly voted to Leave the European Union, would suffer the most harm, according to the forecast.
It predicted after 15 years remaining in the single market would result in UK-wide growth being two per cent lower than current forecasts, securing a trade deal five per cent lower and a no deal eight per cent lower.
The region on course to take the biggest hit is the North East, which was heavily in favor of leaving the European Union. That means thousands upon thousands of job losses.
"This is frankly a nightmare scenario for our region and for the government to be aware of this and still be willing to consider a no deal Brexit is absolute madness".
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.
The Liberal Democrat Brexit spokesman Tom Brake said: "This report confirms that every region and nation will be damaged by Brexit". 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 Tories must explain why they accused the Scottish Government of scaremongering when their own government was covering up similar findings". They are still keeping no deal on the table despite how crippling it would be to the regional economy.
The report, which was leaked amid pressure from Labour and pro-EU Tories, are likely to be seized upon by backers of a "soft" Brexit to protect the economy.
"The public have a right to know, and a right to reverse this if they wish".
A government report on the economic consequences of various Brexit on the UK's GDP over a 15-year period was leaked to the Buzzfeed website last week.
The leak came as MPs were believed to have been seen the assessments in private sessions in the House of Commons on Wednesday. The cabinet sub-committee includes Northern Ireland secretary Karen Bradley, along with the most senior Brexiteers and Remainers in the government.
The SNP government's January report found that a no-deal Brexit would cost the Scottish economy nearly £13bn a year by 2030.
Perhaps even more stark are the effect a no-deal exit would have on retail prices - with the secret analysis suggesting overall high street prices to rise by 21%, and, crucially, food and drink costs to rise by 17%.
Asked during Prime Minister's Questions if she would see off any "threats" from the EU, Mrs May said: 'We will be robust in our arguments.