Dr Susan Hopkins said the R value, or effective reproduction number, of the B.1.1.529 variant in Gauteng in South Africa, where it was first found, was now 2. For an R of anything above 1, an epidemic will grow exponentially.

She voiced her concerns as other countries, including Japan and Germany, joined England and Scotland in banning flights from six countries in the region, while Israel said it had identified its first case with the variant.

Hopkins told BBC Radio 4’s Today programme: “What we’re seeing in South Africa is that they were at a very, very low point, with a very low amount of cases being detected a day, and in a shorter period than two weeks they have more than doubled their epidemiology picture.