MPs are due to vote this week on a tougher tier system in England for when the second national lockdown ends on December 2.

The three-tier approach would see 99% of the country placed in the two highest levels of restrictions.

But when will the restrictions be reviewed and what will be considered when deciding an area’s tier?

– How many people are to face tough restrictions?

More than 55 million people will be placed into Tier 2 and Tier 3 measures on December 2, meaning mixing between households indoors will effectively be banned for the vast majority of the country.

Only the Isle of Wight, Cornwall and the Isles of Scilly – accounting for little more than 1% of England’s population – face the lightest Tier 1 coronavirus restrictions.

Large swathes of the Midlands, North East and North West are in the most restrictive Tier 3, which accounts for 41.5% of the population, or 23.3 million people.

The majority of authorities – including London – will be in Tier 2, which will cover 57.3% of the country, or 32 million people.

– What are the key indicators that will primarily determine the restrictions in each area?

Five factors are considered:
– case detection rates in all age groups;
– case detection rates in the over-60s;
– the rate at which cases are rising or falling;
– the positivity rate – the number of positive cases detected as a percentage of tests taken;
– Pressure on the NHS, including current and projected occupancy.

Downing Street declined to give any further details on the indicators, nor any estimate of the thresholds.

But – in the face of a possible Tory revolt – Boris Johnson has now committed to publish more data and outline what circumstances need to change for an area to move down a tier, as well analysis of the health, economic and social impacts of the measures taken to suppress coronavirus.

– Why are there not rigid thresholds?

The Government has said it needs to maintain flexibility to weigh the indicators against each other – such as whether hospital capacity in neighbouring areas is lower.

Another example given in the coronavirus winter plan is that case detection rates would need to be weighed against whether the spread of the virus is localised to particular communities.

The plan states “given these sensitivities, it is not possible to set rigid thresholds for these indicators, as doing so would result in poorer quality decisions”.

– Is there widespread support for the tier system?

A number of the PM’s Conservative colleagues have been openly critical of the three-tier system.

A crunch Commons vote on the measures on Tuesday could see MPs reject the plan.

Labour shadow foreign secretary Lisa Nandy said her party’s support was “not unconditional” and that it was seeking “clarity” about the tier system.

Without Labour backing – and if Mr Johnson suffers a major rebellion – the Government could struggle to pass its motion on the tier system.

– If the vote is won and the tier system comes into effect, when can any changes be made to it?

The first review of the tiers is set for December 16.

Mr Johnson has said the allocation of tiers will be reviewed every 14 days from that date and suggested mass testing could make households exempt from restrictions.

He also said that at the first review of the measures in mid-December he would move areas down a tier where there is “robust evidence” that coronavirus is in sustained decline.

He has written to Tory MPs offering them another chance to vote on the restrictions early next year, saying the legislation will have a “sunset of February 3”.

That vote after Christmas will determine whether the tier system stays in place until the end of March.

– What are the scientists saying about the prospect of easing measures?

Peter Openshaw, professor of experimental medicine at Imperial College London, said it would be a “terrible mistake” to relax restrictions just months before vaccines “start to have an effect”.

Prof Openshaw, who is a member of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), said: “We scientists are very concerned indeed about relaxation of precautions at this stage. The rates are still too high, there’s too many cases coming into hospitals, too many people dying.

“And if we take the brakes off at this stage, just when the end is in sight, I think we would be making a huge mistake.”