The length of the lockdown depends on how quickly the vaccine is rolled out and how the hospitals are coping.
Lockdown will be reviewed every two weeks, and the Government has a legal obligation to lift the restrictions if they are no longer necessary.
The first mandatory review of the lockdown will take place on January 20, and then there will probably be another one on February 3.
Boris Johnson has said to MPs: “As was the case last spring, our emergence from the lockdown cocoon will not be a big bang but a gradual unwrapping.
“That is why the legislation this House will vote on later today runs until March 31.
“Not because we expect the full national lockdown to continue until then, but to allow a steady, controlled and evidence-led move down through the tiers on a regional basis – carefully.”