The military may be drafted in to airdrop food to the Channel Islands under emergency plans drawn up by the government to protect the UK if a second coronavirus wave coincides with a no-deal Brexit.
A Cabinet Office “reasonable worst-case scenario” document, leaked to The Sun newspaper, also warns the Navy may be needed to stop British fishermen clashing with illegal European fishing boat incursions.
It says parts of the UK may face power and petrol shortages if thousands of lorries are stranded in Dover while shortages of medicines caused by port blockages could lead to animal diseases spreading through the countryside.
The classified document, dated July 2020, further warns that if trade restrictions triggered by a no-deal Brexit are combined with floods, flu and another coronavirus wave, then hospitals may be overwhelmed.
Town halls could go bust and troops may have to be drafted on to the streets if the economic toll causes public disorder, shortages and price hikes, according to the leaked dossier.
A government spokesperson said the document “reflects a responsible government ensuring we are ready for all eventualities”.
UK and EU negotiators warned there has been little progress during the latest round of post-Brexit trade deal talks last week and time is running out to broker a deal before the transition period comes to a close at the end of the year.
Scientists are fearful that the winter months could bring about a second wave of coronavirus in the UK.
Cabinet Office Minister Michael Gove said: “We got Brexit done with a great deal in January and we are working flat out to make sure the United Kingdom is ready for the changes and huge opportunities at the end of the year as we regain our political and economic independence for the first time in almost fifty years.
“Part of this work includes routine contingency planning for various scenarios that we do not think will happen, but we must be ready for come what may.
"Whether we trade with the EU on terms similar to Canada or to Australia, a brighter future awaits as we forge our own path.”
A government spokesperson added: “At the end of the year we will be outside the single market and the customs union, whatever the outcome of negotiations, and intensive planning is under way to help ensure that businesses and citizens are ready to take advantage of the opportunities and changes that will bring.
“This includes launching a comprehensive communications campaign to make sure everyone knows what they need to do to prepare.
“As a responsible government we continue to make extensive preparations for a wide range of scenarios, including the reasonable worst case.
“This is not a forecast or prediction of what will happen but rather a stretching scenario.
"It reflects a responsible government ensuring we are ready for all eventualities.”