Prime Minister Boris Johnson has announced a second national lockdown for England to prevent a "medical and moral disaster" for the NHS.
He said Christmas may be "very different" but he hoped taking action now would mean families can gather.
Pubs, restaurants, gyms and non-essential shops will have to close for four weeks from Thursday, he said.
But unlike the restrictions in spring, schools, colleges and universities can 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.
"No responsible prime minister" could ignore figures which suggested deaths would reach "several thousand a day", with a "peak of mortality" worse than the country saw in April, Mr Johnson said.
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.
Under the new restrictions:
People are being told to stay at home unless they have a specific reason to leave, such as work which cannot be done from home and education
And people are also allowed to leave home for exercise medical reasons, food and other essential shopping and providing care for vulnerable people or for volunteering
Meeting indoors or in private gardens will not be allowed
But individuals can meet meet one other person from another household outside in a public place
Pubs, bars, restaurants and non-essential retail across the nation will close but takeaways and click-and-collect shopping can remain open
Leisure and entertainment venues, including gyms, will also close
Construction sites and manufacturing workplaces can remain open
People are still allowed to form support bubbles
Children can move between homes if their parents are separated
Clinically vulnerable people are asked to be "especially careful" but people are not being asked to resume shielding