Health Secretary Sajid Javid said all flights from South Africa, Namibia, Lesotho, Eswatini, Zimbabwe and Botswana would be suspended as of 12:00 GMT on Friday.
“The first indications we have of this variant are that it may be more transmissible than the Delta variant and that the vaccines we currently have may be less effective,” added Mr Javid.
According to him, British scientists are “very concerned” by this variant, to which South Africa attributes the recent increase in cases recorded in the country and which has also been detected in travelers from Botswana or Hong Kong.
However, no case has been recorded in Great Britain.
“We will ask anyone arriving from these countries from 4:00 am Sunday to quarantine themselves in hotels,” Javid said, adding that those arriving before that date will have to self-isolate and do two PCR tests at second and eighth day of their confinement.
“And if someone has arrived from these countries in the last ten days, we will ask them to do PCR tests,” he added.
Britain has been among the countries hardest hit by Covid-19, with 144,000 deaths since the start of the pandemic.
The number of cases remains high – more than 47,000 in the past 24 hours on Thursday – but more than 80% of people aged 12 and over have received a double injection of the vaccine, and almost 30% have had a third dose.
The UK government has come under heavy criticism for delaying tightening travel restrictions at the start of the pandemic, when it kept its borders open as infection rates skyrocketed.