The British government had no choice but to cancel plans for a relaxation of rules over the Christmas period and strict measures to control the novel coronavirus could remain in place "until a vaccine is rolled out", said Health Secretary Matt Hancock on Sunday.
Under new Tier 4 rules, around one-third of the population of England is now forbidden from spending Christmas with other households after Prime Minister Boris Johnson on Saturday abandoned plans to allow five-day gatherings, having previously defended the festive relaxation policy.
The tough new rules were quickly brought in when government scientists presented ministers with evidence of a new variant of the virus that makes it 70 percent more transmissible than other strains in circulation.
Asked whether the virus was under control, Hancock told the BBC's Andrew Marr program: "No it's not, the new variant is out of control and we need to bring it under control."
He said it was "important for everybody to act like they might have the virus".
He added: "We don't want to do any of this but it is necessary. On Friday, when we were presented with that new scientific evidence about the new variant, it was our duty to act.
"We acted very quickly and decisively with the announcements the prime minister set out yesterday."
Immediate new Tier 4 restrictions introduced in large parts of the country, including in London, the southeast and areas of eastern England, canceled festive plans for millions of people. Non-essential retail will close, as will indoor leisure and entertainment.
The measures are due to be reviewed after two weeks, though Hancock suggested they could remain in place "for the next couple of months".
"Cases have absolutely rocketed, so we've got a long way to go," Hancock told Sky News' Sophy Ridge on Sunday program.
He said: "It is an enormous challenge, until we can get the vaccine rolled out to protect people. This is what we face over the next couple of months."
Hours after the policy announcement on Saturday, there were scenes of crowding at London train stations, as people rushed to leave the capital before the rules came into force, something Hancock called "totally irresponsible".
London Mayor Sadiq Khan said the U-turn was a "bitter blow" for families and businesses, and that the indecision shown by the government in the last week has now "led to so much anguish, despair, sadness and disappointment".
"I'm afraid it makes it really difficult for people like me to ask people to listen to us when we keep on changing our minds," he told the BBC's Breakfast program on Sunday.
Opposition Labour leader Keir Starmer said on Twitter: "At this time of national crisis, the British people want clear, decisive leadership. All we get from Boris Johnson is confusion and indecision."
The Confederation of British Industry, or CBI, called the new rules a "real kick in the teeth" for many businesses.
The CBI's chief UK policy director, Matthew Fell, told Reuters that the government now must take a "fresh look" at how to support UK businesses through to the spring. British companies are also facing the uncertainty of a possible no-deal Brexit departure from the European Union on Dec 31.
More European countries are considering immediate bans on incoming flights from the UK, Sky News reported, after Belgium on Sunday joined the Netherlands in banning air travel from Britain due to fears over the new strain of the coronavirus. Germany is reportedly also considering a UK travel ban.
Dutch health authorities confirmed at least one case of the same variant and the Netherlands said it will assess "with other EU nations the possibilities to contain the import of the virus from the United Kingdom".