The Government has implemented a travel ban on passengers arriving in England from South Africa after two cases of another new strain of Covid-19 linked to the country were identified in the UK.
Health Secretary Matt Hancock warned the "highly concerning" new variant is believed to be more transmissible than the mutant strain that resulted in the creation of the new Tier 4 restrictions.
It is believed to be behind an increase in cases in South Africa, and has been discovered in two people in the UK thought to be contacts of those who travelled between the two countries in the last few weeks.
From 9am on Christmas Eve, visitors arriving into England who have been in or transited through South Africa in the previous 10 days will not be permitted entry and direct flights will be banned, the Department for Transport (DfT) said.
The ban excludes cargo and freight without passengers, and also does not include British and Irish nationals, visa holders and permanent residents, who will be able to enter but are required to self-isolate for 10 days along with their household.
Any exemptions usually in place – including for those related to employment – will not apply and passengers arriving in England from South Africa after 9pm on Wednesday cannot be released from self-isolation through Test to Release.
At a Downing Street press briefing on Wednesday afternoon, Mr Hancock said: "This new variant is highly concerning because it is yet more transmissible and it appears to have mutated further than the new variant discovered in the UK."
He added: "Anyone in the UK who has been in South Africa in the past fortnight and anyone who is a close contact of someone who has been in South Africa in the last fortnight, must quarantine immediately.
"They must restrict all contact with any other person whatsoever."
The ban and expanded self-isolation measures will be kept under review, the DfT said.
The "UK" strand of the coronavirus is believed to have mutated randomly in Kent as early as September, and prompted the Prime Minister to abandon the proposed relaxation of restrictions over Christmas.
Latest figures suggest the South African strain was behind a record number of people being taken to hospital there.