The U.K. is facing the threat of critical food shortages, including for fresh fruit and vegetables, just days before Christmas, as European countries impose bans on transit from the country in response to the discovery of a mutant strain of coronavirus in southern England.

The French government imposed a 48-hour ban on both people and trucks coming into the country from the U.K., starting today. The decision is likely to cripple U.K. trade with the rest of Europe, much of which crosses between Calais, in France, and Dover[/hotlink], in England.

The potential food shortages are a grim irony for a country that had been racing to meet a December 31 deadline to secure a trade deal with the European Union that was meant to prevent exactly such a prospect.

The English Channel crossing between Dover and Calais handles up to 10,000 trucks per day, 90% of all truck traffic entering the country. About half of all British imports cross that border. In addition, about 50% of the food Britons consume—and up to 85% of the fresh fruit and vegetables the country eats—come from the EU, much of it shipped by trucks which cross the English Channel on ferries or the Eurotunnel train from France.

While there is no ban on these trucks arriving in Britain, many freight haulers are reluctant to send drivers to the U.K. without the certainty of knowing they will be able to make the return crossing back to mainland Europe.

British Prime Minister Boris Johnson on Monday was planning to hold emergency talks with his government ministers on how to ensure the continued flow of freight into the country. Meanwhile, European Union officials were holding a crisis committee meeting to coordinate response to the new mutant coronavirus variant.

In addition to France, Austria, Belgium, Finland, Germany, Ireland, Italy, and the Netherlands have all blocked U.K. arrivals. Further afield, Israel turned back visitors arriving from the U.K. and Hong Kong banned flights from Britain in response to the new mutant strain.

The new variant of SARS-CoV-2, the virus that causes Covid-19, has emerged in southern England in recent weeks. British government scientists said on Saturday that tests had shown the new strain was 70% more transmissible than the original virus. But they said there was no evidence so far that the new variant was more likely to cause serious illness or that the current crop of Covid-19 vaccines being rolled out across the world would not protect against it.

The imposition of travel bans on British citizens seems to have largely been the result of the Johnson government's own sudden decision on Saturday to impose stringent restrictions on movement, socializing and business for large parts of southern England, where the new strain is most prevalent. That move was a sharp U-turn for Johnson, who had imposed a national lockdown in November in an effort to stem a huge spike in infections, centered largely in the north of England, and had been planning to relax social distancing measures over the Christmas holidays.

Parts of the U.K. government seem to have been aware of the new strain for some time. British labs first detected in early October in a sample taken from someone in late September. But concern about the mutant strain seems to have been subdued until the U.K. began experiencing a massive second wave of Covid-19 infections in October and November. With new cases totaling more than 25,000 people per day by early December, scientists realized that the new strain was now responsible for a large number of these—accounting for the majority of new cases in London and eastern England and about half of those in southeast England.

Matt Hancock, the U.K. health minister, first mentioned the new strain publicly in a speech to Parliament on December 14. He said at the time that the World Health Organization had been notified about the new variant. But Hancock said that it was not until Friday that he and Johnson and a wider group of ministers were fully briefed on the alarming figures about the increased transmissibility of the new strain by an expert advisory group that works on new and emerging respiratory virus threats.

The new travel bans also comes at a critical moment in negotiations between the U.K. and the EU on an agreement to govern their trading relationship after December 31, when a one-year Brexit transition period expires. Despite years of talks, negotiators have so far failed to reach a deal—and missed another deadline for reaching one on Sunday as disagreements between the two side remained on issues such as fishing rights.

Without a deal in place, the U.K. will likely face chaos along the Dover-Calais trucking route, with new paperwork and customs checks likely leading to miles-long tailbacks on both sides of the English Channel, and warnings these delays could lead to food shortages. As a result, many retailers and grocers have been attempting to stockpile supplies in advance of January 1 and the road approaches to the Channel crossings have already been congested for weeks due to the additional truck traffic.