The document was meant to be shown confidentially to cabinet ministers this week but was leaked in an embarrassing development for Theresa May and David Davis, the Brexit secretary.
It said national income would be 8% lower under a no deal scenario, around 5% lower with a free trade agreement with the EU and about 2% lower with a soft Brexit option of single market membership over a 15-year period.
The government would not comment on leaked documents but sources stressed the analysis did not cover May’s preferred option of a bespoke deal amounting to a “deep and special partnership” with the EU.
The document suggested that chemicals, clothing, manufacturing, food and drink, and cars and retail would be the hardest hit and every UK region would also be affected negatively in all the modelled scenarios, with the north-east, the West Midlands and Northern Ireland facing the biggest falls in economic performance.
It comes after Davis refused to release impact assessments covering 58 sectors of the economy when requested to by parliament, claiming they did not in fact exist.
Remain supporters said the report, seen by BuzzFeed News, was concerning but in line with what they had feared.
Stephen Gethins, the SNP’s Brexit spokesman, said: “This is highly embarrassing for Theresa May, but for those of us working to ensure the UK stays in the single market and customs union, this is not surprising.”
The report prompted Chris Leslie, a Labour MP and supporter of the Open Britain group campaigning against a hard Brexit, to call for the public release of the document. “It’s little wonder the government has repeatedly refused to publish any serious Brexit analysis,” he said. “Their own impact assessments underline what has long been obvious, that their reckless plan to crash out of the single market and the customs union will leave us all much worse off.
“There is no mandate for this hard and destructive Brexit. No one voted to make themselves or their families worse off.”
Eloise Todd, the chief executive of anti-Brexit organisation Best for Britain, added: “According to the government’s secret analysis, even the softest Brexit scenario will mean a 2% hit to growth.
“Almost every community, region and sector of the economy included in the analysis would be negatively impacted. The case for or against Brexit should be about more than balance sheets, but it’s painfully clear that the numbers are a gloomy part of the story. And behind these numbers are thousands of jobs, businesses and homes that are at risk.
“The government are calling this document embarrassing but it’s more than that. It is a colossal act of economic self harm, written down clearly, in black and white. We are reading about an economy facing the abyss.”
A government spokesperson said: “We have already set out that the government is undertaking a wide range of ongoing analysis in support of our EU exit negotiations and preparations. “We have been clear that we are not prepared to provide a running commentary on any aspect of this internal work and that ministers have a duty not to publish anything that could risk exposing our negotiation position.”