The Prime Minister told the country to stay indoors other than for limited exceptions, such as shopping for necessities including food and medicine, and to work from home unless it is impossible to do so.
He said the lockdown will become law in the early hours of Wednesday, while MPs will retrospectively be given a vote after they are recalled early from the Christmas break, but the public should follow the rules immediately.
So what are the rules? Here’s everything you need to know.
Can you exercise outdoors with a friend?
It is fine to go for a walk or a run with one friend from another household. But lingering for a chat or a drink in the park is not allowed.
What about professional sports?
Sports which like Premier League have well organised testing and safety procedures will be able to carry on.
Will GCSE and A Level exams go ahead?
This is going to be discussed. It is currently seen as unlikely that they will go ahead as originally envisaged but details of what could happen are not yet available. B Tech exams due in the next few days will, however, go ahead.
Can a trades person or a cleaner come into my home?
Yes, unlike in the first lockdown, people can enter a home for the purpose of work. But strict care and social distancing rules must be applied by you and the tradesperson.
Do these rules even apply in the Isles of Scilly, currently in Tier One?
Yes, this is a national lockdown and applies to all.
Can alcohol be sold only in shops or online?
Yes, the sale of takeaway booze is not going to be allowed because in the first lockdown, takeaways tended to be abused by al fresco gatherings of drinkers.
What about infants’ nurseries and early years centres?
They can stay open, subject to strict protocols.
Can dentists and opticians stay open?
Yes, they are allowed to treat people.
Can we visit our holiday home?
No. Just as last year, unessential travel is not allowed and that includes keeping away from second homes.
Is driving to exercise allowed?
The requirement is to stay local and not to go on long cross-country trips for leisure.
Can churches or temples hold services?
Yes, places of worship can hold services with social distancing.
Can we go skiing?
Not during this lockdown. Essential journeys only are allowed.
How often can we exercise outside?
Once a day only during the lockdown. And you should stay local.
Can children travel between the households of divorced or separated parents?
As in last year, children will not have to choose but can switch from one household to another.
Do support bubbles continue?
Yes, support bubbles and childcare bubbles will continue.
What about people who were asked to shield last time?
People who are clinically extremely vulnerable should stay at home as much as possible. They should only leave home for exercise and should avoid shops, including pharmacies. No announcement has been made yet on whether they will get extra support, such as the Boris Boxes of food delivered last time.
Can I go to work in my office?
You must work from home if that is possible. But people like construction workers who cannot work from home can go to work.
Can I go shopping?
Only for essentials, like food and medicines.