The UK identified a second new mutant strain of Covid-19, with links to South Africa, as millions more people face tighter restrictions to help curb the virus.
Britain's Transport Minister Grant Shapps ordered flights and arrivals from South Africa to be halted after a potentially more infectious variant of the novel coronavirus that causes Covid-19 had spread to Britain.
"I've taken the decision to temporarily stop flights and arrivals entering England from South Africa from 9am tomorrow following an outbreak of a new strain of coronavirus," he said.
Health Secretary Matt Hancock said at least two people in the UK were infected with the "highly concerning" variant that emerged from South Africa.
"Thanks to the impressive genomic capability of the South Africans, we've detected two cases of another new variant of coronavirus here in the UK," Mr Hancock said. "Both are contacts of cases who travelled from South Africa over the past few weeks."
He said that the South African strain is even more infectious than the VUI-202012/01 variant which was announced by Boris Johnson last weekend, and said to be 70 per cent more infectious than the most common type.
"This new variant is highly concerning, because it is yet more transmissible, and it appears to have mutated further than the new variant that has been discovered in the UK," Mr Hancock said on Wednesday.
South Africa's health department said last week that a new genetic mutation of the virus had been found and might be responsible for the country's recent surge in infections.
Anyone who has been to South Africa, or has been in close proximity to someone who has travelled there, must go into quarantine, the Health Secretary said.
Mr Hancock also said the government would extend tough tier four measures across many areas of Britain from midnight on Boxing Day.
Sussex, Oxfordshire, Suffolk, Norfolk, Cambridgeshire, most of Hampshire and the remainder of Essex will now follow London and parts of the south-east into the highest level of restrictions.
Mr Hancock did not say whether a full lockdown in England was being considered, but said that thanks to these additional steps "brighter skies" were ahead.
Earlier on Wednesday, Communities Secretary Robert Jenrick said the variant was a “significant game changer” and hinted that current lockdown measures are not enough to halt its spread.
“The number of cases is rising and the variant is spreading to other parts of the country,” he said. “So we will see whether it’s necessary to do more and make sure that the tiered system is sufficiently robust for the new circumstances.”
Researchers say the VUI-202012/01 variant has been found in Wales and Scotland, while health chiefs in the northern English counties of Cumbria and Lancashire believe the mutation is responsible for the sharp rise in cases there.
Labour leader Sir Keir Starmer wrote to the prime minister to say his party would back any new lockdown measures.
Irish political party Sinn Fein called on an island-wide shutdown to stop the spread of the disease, a move that is likely to be resisted by their Northern Ireland power-sharing partners in the Democratic Unionist Party.
Northern Ireland is already under lockdown for the next six weeks, while Wales and Scotland are planning to introduce tighter measures within days.
Meanwhile, hauliers have been told to avoid travelling to Dover where more than 2,800 lorries were stuck on Tuesday afternoon.
France has finally agreed to lift a two-day blockade and allow heavy goods vehicles into the country, but will require people arriving to pass a Covid-19 test no more than 72 hours beforehand.
The protocol agreed with the French government will be reviewed on December 31 but could run until January 6, the Department for Transport said. Those who can make journeys include French citizens, hauliers and British citizens living in France.
UK Transport Secretary Grant Shapps said it could take until Christmas for congestion to clear near ports struggling to deal with the huge backlog.
Emotions are running high in the area, with reports of confrontations between drivers and a small number of police officers.
TV footage showed lorry drivers honking their horns and flashing lights in unison in the dark, while in the early hours of the morning many gathered in the roads around the port to vent their frustration and question officials and police.
Elizabeth de Jong of Logistics UK said it was vital that testing procedures are put in place quickly “to ensure drivers can be processed and get home for Christmas safely”.
“The backlog of traffic across the region will take time to clear so hauliers should wait for further news before travelling to Kent,” she said.
The episode prompted a new wave of panic-buying in UK shops as customers stripped shelves in some supermarkets of turkey, toilet rolls, bread and vegetables.
Retailers Tesco and Sainsbury's both said food supplies would be affected if the disruption continued. Tesco said it had imposed temporary buying limits on some essential products.
Experts appearing at the Science and Technology Committee on Wednesday said they are now “almost certain” that the new variant of the virus is more infectious. Prof Peter Horby, chairman of the Nervtag advisory committee, said he did not believe the government had overstated the danger posed by the new variant.
On Wednesday, a further 744 people died in the UK within 28 days of testing positive for Covid-19. A record number of new infections was also reported, with 39,237 testing positive for the disease.
Meanwhile, Scottish First Minister Nicola Sturgeon was forced to apologise after she was spotted without a mask at a funeral. The Scottish National Party leader took off the covering temporarily at a wake for a government official, according to The Sun newspaper.
“This was a stupid mistake and I’m really sorry,” Ms Sturgeon told the BBC. “I talk every day about the importance of masks so I’m not going to offer any excuses.”
Other European countries are looking at ways to tackle the new mutation before it spreads uncontrollably in their borders.
Travellers wanting to fly to the Netherlands will be required to have tested negative for Covid-19 no more than three days before departure as of next Tuesday, the Dutch government said.
The requirement was already in force for travellers from Britain and South Africa.