MPs will vote on Tuesday whether to approve Boris Johnson’s three-tier system of coronavirus restrictions.

If the government wins, the new rules replacing England’s national lockdown will come into force from Wednesday December 2.

Under the system, the country will be split into tier 1, tier 2 and tier 3.

In total, almost 99% of England’s population will enter tier 2 or 3, with tight restrictions on bars and restaurants and a ban on households mixing indoors.

Only the Isle of Wight, Cornwall, and the Isles of Scilly will be under the lightest tier 1 controls, while large swathes of the midlands, north east and north west are in the most restrictive tier 3.

How long will the tiered system last?

The government has said it wants the tiers, which are stricter than those in place before the national lockdown, to be in place until the end of March 2021. Boris Johnson told Tory MPs in a letter on Saturday this would be “necessary to control the virus through the winter”.

Could it end sooner?

Yes. In a move to appease his MPs, the prime minister has promised the system will have a legal “sunset” of February 3. This means in order for the tiered approach to remain in place beyond then, parliament would have to vote in favour of it again.

Can regions change tiers and when?

Yes. The government will review the tiers in each region of England on December 16. Any changes will be announced on Thursday December 17 and will come into effect on Saturday December 19.

The government’s Joint Biosecurity Centre and ministers will look at the data across England on a weekly basis from then on.

Chris Whitty, the chief medical officer, will chair a meeting on Tuesdays. Matt Hancock, the health secretary, then chairs a meeting on Wednesdays for Thursday announcements on any changes to the tiers.

There is also a specific requirement in the legislation to conduct a formal review of the tiering allocations every fortnight.

How can a region move down tiers?

The government has said it will base any decision on whether a region needs to move up or down tiers on five criteria. 

• Case detection rates in all age groups;

• Case detection rates in the over 60s;

• The rate at which cases are rising or falling;

• Positivity rate (the number of positive cases detected as a percentage of tests taken);

• Pressure on the NHS.

Ministers will also consider local views “to build the most accurate picture” of what is happening on the ground.

Will the types of areas change?

The government is largely imposing restrictions on entire counties, with some exceptions.

But many Tory MPs are unhappy with such a broad-brush approach and want more localised interventions to prevent local authority areas with low infectionrates being lumped together with ones with a high rate.

Johnson said “every local authority area and each region” would be looked at when the tiers are reviewed.

But Dominic Raab told Times Radio on Sunday that the government would stick to its county by county system. “That’s the approach we’re taking. Yes,” he said.

Why are the new tiers stricter than the old tiers?

In short, the government decided the old tiers simply were not working. The Scientific Advisory Group for Emergencies (Sage) told ministers stronger measures would be needed to prevent the epidemic from growing.

Its analysis showed that tier 1 measures were not able to stop the growth of the virus, tier 2 managed to slow but not reverse the pace of growth, and tier 3 managed to get cases falling in most, but not all, areas.

What about the Christmas holiday?

The vote on Tuesday will also include whether to approve the government’s plan to loosen restrictions over Christmas.

Under the plan, which applies across the UK, up to three households to form an exclusive “bubble” to meet at home and go to places of worship during the period between 23 and 27 December.