A hard border would be required on the island of Ireland in the event of a no-deal Brexit, according to the British government.
Official documents leaked to the Sunday Times show Downing Street expects a return to border checks as current plans to avoid them will prove "unsustainable".
The documents also show Britain will face shortages of fuel, food and medicine if it leaves the EU without a transition deal.
The newspaper said the forecasts set out the most likely aftershocks of a no-deal Brexit rather than worst-case scenarios.
Meanwhile, the Mail on Sunday reported that British Prime Minister Boris Johnson has accused the UK's former chancellor Philip Hammond of “gravely damaging” the national interest with his bids to frustrate Brexit.
In a letter seen by the paper, the PM said it was “plain as a pikestaff” that the EU “will simply not compromise as long as they believe there is the faintest possibility that Parliament can block Brexit on 31 October”.
The Sunday Telegraph reported a Downing Street source accusing Tory Remainers of “appalling dishonesty” for attempting to use the Brexit delay to “cancel the referendum”.
The paper also said that Brexit Secretary Stephen Barclay has signed the “commencement order” that will trigger the end of the supremacy of EU law in the UK on October 31.
