A no-deal Brexit could lead to shortages of food, fuel and medicine, as well as a hard border on the island of Ireland, according to leaked official government documents published in the Sunday Times.
The newspaper said the forecasts compiled by the Cabinet Office under the codename Operation Yellowhammer set out the most likely aftershocks of a no-deal Brexit rather than the worst case scenarios.
It comes ahead of Prime Minister Boris Johnson's first EU trip this week during which he will demand a new withdrawal agreement and warn how serious he is about pursuing a no-deal Brexit if he does not get one.
The dossier shows that 85% of lorries using the main channel crossings "may not be ready" for French customs, meaning disruption at ports would potentially last up to three months before the flow of traffic improves, the Times said.
The government also believes a hard border between Northern Ireland and the Republic will be likely as current plans to avoid widespread checks will prove unsustainable.
The Times said: "The dossier offers a rare glimpse into the covert planning being carried out by the government to avert a catastrophic collapse in the nation's infrastructure.
"The file, marked 'official-sensitive' requiring security clearance on a 'need to know' basis is remarkable because it gives the most comprehensive assessment of the UK's readiness for a no-deal Brexit."
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Mr Johnson has repeatedly vowed to leave the EU on 31 October with or without a deal.
More than 100 MPs have urged Mr Johnson to immediately recall parliament and let it sit permanently until Britain's exit.
Responding to the leaked document, minister Kwasi Kwarteng dismissed a rise in "scaremongering" about no-deal.
"'A lot of people are playing into project fear and all the rest of it," he told Sky News' Sophy Ridge on Sunday.
Tory former ministers Dominic Grieve and Guto Bebb were among the signatories of a letter sent to the prime minister this weekend which claims a "creeping and disturbing populism" is taking over his discourse with the EU.
The Westminster leaders of the SNP, Liberal Democrats, Plaid Cymru, Change UK, and the Green Party's Caroline Lucas also backed the call, along with several Labour MPs.
They wrote: "Since the SecoRead More – Source