On Saturday evening, Boris Johnson announced a second national lockdown for England in order to prevent a "medical and moral disaster" for the National Health Service.
Christmas, the prime minister said, may be "very different", but he hoped taking action now would mean families can gather.
Non-essential shops and hospitality will have to close for four weeks from Thursday, but unlike the restrictions in the spring, schools, colleges and universities will be able to stay open.
The new measure will come in on Thursday, and after 2 December, the restrictions would be eased and regions would go back to the tiered system, the prime minister said.
Boris Johnson added: "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."