British Health Secretary Matt Hancock said Sunday that the government has imposed a strict Christmas lockdown in London and southeast England because a new strain of the coronavirus was "out of control".
Hancock warned that the strict measures that affect almost a third of England's population could stay in place until the virus vaccine is fully rolled out.
"We acted very quickly and decisively," Hancock told Sky News, justifying the "stay at home" order, ban on family gatherings over Christmas and closure of non-essential shops.
"Unfortunately the new strain was out of control. We have got to get it under control."
Prime Minister Boris Johnson announced on Saturday that millions must cancel Christmas plans and stay home because the new strain was spreading far more quickly.
Around 16.4 million people entered the strictest "tier four" measures from Sunday, or 31 percent of England's population.
They are not allowed to hold family gatherings for Christmas, while in the rest of the country households are allowed to mix on Christmas Day alone.
London's Metropolitan Police said that it would take action against those who "make reckless decisions that risk lives."
Other UK regions have also tightened their anti-virus measures in response.
Wales introduced a strict lockdown from Sunday, while Scotland has banned travel to and from other UK regions for Christmas. Both Scotland and Northern Ireland will enter fresh lockdowns on December 26.
Hancock told Sky News that the situation was "deadly serious."
"It's going to be very difficult to keep it under control until we have the vaccine rolled out," he said, adding: "This is what we face over the next couple of months."
The UK hopes to reach a figure of half a million vaccinations over the weekend, the health minister said.
Scientists first discovered the new variant in a patient in September, Susan Hopkins of Public Health England told Sky News.
She said that scientists in November found the new strain was behind a cluster of cases in Kent and spreading into London and Essex and informed the government on December 11.
Public Health England then again notified the government on Friday when modelling revealed the full seriousness of the new strain, she said.
She confirmed the figure given by Johnson that the new virus strain could be 70 percent more transmissible while saying this was an initial figure.
"I think 70 percent looks like a good number to land on at the moment," she said.
The virus has been found in all regions of England but in small numbers, Hopkins said.
Hancock said cases have also been identified in Australia and Europe.
Patrick Vallance, the government's chief scientific adviser, said Saturday that the new strain "contains 23 different changes," including to the way the virus binds to human cells and enters cells.
London Mayor Sadiq Khan told Sky News that London now has the same number of inpatients with the virus as during the peak of the first wave in April. Cases have also grown rapidly among those aged 10 to 19, he said.
Paul Hunter, professor in medicine at the University of East Anglia, told the Observer weekly that "if this new variant is behind the increase in this age group, then that is a big worry."
- PM 'scared' - The grave situation prompted widespread criticism of the prime minister for promising last week not to "cancel Christmas."
"Not much was understood about this mutant virus. But that uncertainty should have been enough for the PM to see that then was the time to call off Christmas," wrote The Sunday Mirror weekly.
Labour Leader Keir Starmer said in a video statement: "We have a prime minister who is so scared of being unpopular that he is incapable of taking tough decisions until it is too late."
Some Londoners backed the lockdown measures.
"See I think it's the right move at the moment," said Marcel Hadula.
"We don't want to overwhelm the NHS, because if we do that, then how can we effectively treat everybody that will come into contact with this new strain of the Covid virus?"
But Chiara Morreale said her relatives were likely to break the lockdown rules over Christmas.
"On Christmas (Day) there's a good chance, my auntie and uncle will come around," she said.