Prime Minister Boris Johnson has announced a second national lockdown for England as the UK passed one million Covid-19 cases.
He said the steps were necessary to avoid the “medical and moral disaster” of the NHS being overwhelmed.
Non-essential shops and hospitality will have to close for four weeks on Thursday, he said.
But unlike the restrictions in spring, schools, colleges and universities will be allowed to stay open.
After 2 December, the restrictions would be eased and regions would go back to the tiered system, he said.
Mr Johnson said: “Christmas is going to be different this year, perhaps very different, but it’s my sincere hope and belief that by taking tough action now we can allow families across the country to be together.”
The prime minister told a Downing Street news conference that he was “truly, truly sorry” for the impact on businesses, but said the furlough system paying 80% of employee wages will be extended through November.
He said hospitals even in the south-west of England, where cases are among the lowest, will run out of capacity in weeks.
“Doctors and nurses would be forced to choose which patients to treat, who would get oxygen and who wouldn’t, who would live and who would die,” Mr Johnson said.
Takeaways will be allowed to stay open as pubs, bars and restaurants close and people are being told they can only meet one person from outside their household outdoors.
Mr Johnson, who chaired a cabinet meeting on Saturday afternoon, will make a statement to Parliament on Monday.
The UK recorded another 21,915 confirmed coronavirus cases on Saturday, bringing the total since the pandemic began to 1,011,660.
Another 326 people were reported to have died within 28 days of a positive test.
The UK is the ninth country to reach the milestone of a million cases – after the US, India, Brazil, Russia, France, Spain, Argentina and Colombia.
But the true number of infections is expected to be higher due to a lack of widespread testing at the start of the pandemic.
Graphic showing UK coronavirus figures
Prof Neil Ferguson, whose modelling was crucial to the decision to impose the first lockdown, said keeping universities and schools open meant infections would decrease more slowly this time.
He said the new restrictions could reduce cases by anywhere between 20% and 80%, adding that he hoped larger groups of people would be able to gather by Christmas “if only for a few days”.
Mr Johnson had previously resisted pressure to introduce nationwide restrictions, saying they would be “disastrous” for the UK’s finances and opting instead for a three-tiered system targeting local areas in England.
Ahead of the news conference, school and university unions called for education institutions to be closed and for teaching to move online in another national lockdown.
The National Education Union said it would be “self-defeating” to ignore how schools helped to spread the virus.
And “the health and safety of the country is being put at risk” by the insistence on keeping in-person teaching on campuses, the University and College Union said.