Civil servants have drawn up scenarios for the worst cases of what would happen in the event of a “no deal” with Brussels.
And the research, leaked to the Sunday Times, includes models for mild, severe and “Armageddon” reactions to no-deal exits.
It quoted a source as saying that even the severe scenario saw the Port of Dover “collapse on day one”.
But the Department for Exiting the EU has dismissed the claims and prominent Leavers have blasted the report on social media.
Leave campaigner Douglas Carswell suggested the predictions indicated a lack of imagination from the civil service.
He tweeted: “Whitehall leaks on Brexit domesday tell us more about Whitehall mindset than Brexit.
“If you are a civil servant who presumes human social and economic affairs need to be organised by bureaucratic fiat, you cannot conceive how things might work without such fiat.”
And Matthew Lesh, an Australian research fellow at the Institute of Public Affairs, pointed out: Australia isn’t a member of the EU, and yet somehow our supermarkets are filled with food.
“Australia trades with the EU on WTO terms, we have no free trade agreement – and yet we still trade billions of dollars with the EU every single year.”
Julia Hartley Brewer raged: “It’s almost as if no countries actually exist (and thrive) outside of the European Union.
“Apart from, oh, almost every sodding country in the entire world – including most of the G20. Get a grip.”
And another Leave voter wrote: “If Remoaners think they are helping their cause by rallying behind the Doomsday Brexit article they are even more deluded than previously thought.
“They are simply showing en masse how desperate, gullible and dishonest they are.
“Literally everyone else can see through them.”
Another wrote: “They just can’t give up on Project Fear can they?”
Home Secretary Sajid Javid said today he did not recognise the “doomsday” scenarios.
He told the BBC’s Andrew Marr Show: “I have to say I don’t recognise any bit of that at all and as Home Secretary.
“I am deeply involved in ‘no deal preparations’ as much as I am in getting a deal – I’m confident we will get a deal.
“From the work that I have seen and the analysis that has been done, those outcomes, I don’t think any of them would come to pass.”
He added that the Government was making progress with Brexit plans, saying: “I’m confident that as we get to the June council meeting the Prime Minister will have a good set of proposals and our colleagues in Europe will respond positively.”