France is to keep in place restrictions on its border with Britain "until further notice", Prime Minister Jean Castex said Thursday, after the country confirmed two clusters of the mutant UK coronavirus variant.France closed its border with Britain on December 20 after the emergence of a new UK strain of the disease, thought to be far more contagious, and "this will be extended until further notice", Castex said.Also Read | The faces behind the farmer revoltOnly certain categories of people, including truck drivers, are allowed through the border providing they have can show a negative PCR test during the three preceding days.Also Thursday, the French health ministry reported that two clusters of the UK variant had been detected in a care.