The civil service has drawn up plans for the introduction of martial law in the event of a chaotic no-deal Brexit, it has been reported.
According to the Sunday Times, officials have gamed a state of emergency and the use of powers under the Civil Contingencies Act to crack down on disorder if the UK is plunged into turmoil without a Brexit deal.
Measures available under that law include travel bans, curfews and the deployment of the armed forces on the streets of Britain - while ministers would be able to amend any act of Parliament except the Human Rights Act for up to 21 days.
A Downing Street spokesperson said: "Respecting the referendum decision means leaving the EU.
"The PM has said that there will be disruption in the event of no deal, but as a responsible Government we are taking the appropriate steps to minimise this disruption and ensure the country is prepared."
A source told the Sunday Times: "As no-deal preparations are accelerated and training is rolled out to civil servants, questions have been raised about the legislation and how it could be used in the event of a no-deal Brexit."
It came as a serving minister demanded that Theresa May removes the threat of a no-deal Brexit – the default position if Parliament does not back a deal with the European Union by March 29 – as MPs prepare to vote on alternatives to her agreement with the EU.
Writing in the same paper, defence minister Tobias Ellwood – who voted to Remain in the EU 2016 – said: "It is now time to rule out the very possibility of no deal.
"It is wrong for government and business to invest any more time and money in a no deal outcome which will make us poorer, weaker and smaller in the eyes of the world."
May has repeatedly warned that the only way to avert a no-deal Brexit is to back her deal, although MPs will next week vote on plans to request an extension of Article 50 – a move which would postpone leaving without an agreement.
The intervention from Ellwood comes just days after business minister Richard Harrington openly challenged the prime minister to sack him after he said the threat by Airbus to quit the UK proved a no-deal Brexit would be a "disaster".
And in a report released today the cross-party Exiting the European Union Select Committee said a no-deal Brexit "cannot be allowed to happen".
The report said MPs "must" be given the chance to vote on extending Article 50, delaying the UK's exit from the bloc to stave off leaving without an agreement.
The Commons will on Tuesday be asked to cast its verdict on a string of alternatives to May's deal – including asking for an Article 50 extension – after her agreement was roundly rejected in an historic Commons vote earlier this month.
However, the committee said a "lack of transparency and a lack of time" had undermined Whitehall's ability to get ready for a no-deal exit, and said it was "deeply concerned" about the readiness of business for Britain failing to sign off on an EU deal.
They warned: "Brexit was always going to lead to change for business with a range of new challenges but also opportunities.
"However, businesses have had no certainty about what to prepare for and, in the event of a no-deal exit would face an abrupt change in trading circumstances which would represent a cliff edge for many—an abrupt change which concerned our predecessor Committee two years ago for which, it is clear, many businesses have not prepared."
The group of MPs said a no-deal exit, which is likely to see the UK face tariffs on goods traded with European countries for the first time in decades, could have a "very significant impact" on Britain's ability to compete around the world, with agriculture particularly hard hit.
They also raise concern that the government's planning for a no-deal has relied on "assumptions" about how the EU will respond which are at odds with what businesses believe will happen.
"There appears to be no majority in the House of Commons in favour of a no deal exit, although that remains the default outcome if the House of Commons is unable to approve the deal that has been reached or pass the legislation required to implement it in domestic law," the committee said.
"While the EU might agree to side deals to mitigate the worst of the disruption of a no deal outcome, this cannot be guaranteed, and we are concerned by the extent to which assumptions of an ongoing cooperative relationship underpin the government’s no deal planning. Since these assumptions cannot be guaranteed, a 'managed no deal' cannot constitute the policy of any responsible government."