NOW that Warrington has entered the 'very high' Covid alert level, it will have to prove a range of factors to move down to a lower tier.

This includes a 'stabilisation of case rates' and the confidence that NHS workers have the ability to retain key services.

The latest case rates in Warrington show 830 new cases for the seven-day period leading up to October 22, representing 395.2 cases per 100,000 residents.

Is there a set of criteria for a region moving up or down a tier?

There is no published criteria on what factors lead to an area being moved from one tier to another.

But, Dr Clare Gardiner, director general of the Joint Biosecurity Centre (JBC), said there is a 'basket of indicators' looked at with the chief medical officer, who then makes recommendations to ministers.

Do we know what factors are considered?

Dr Gardiner outlined a range of indicators for a region moving up to tier three, including having a rate of more than 100 to 150 coronavirus cases a week per 100,000 population, case rates in the over 60s, having a positivity rate of more than 7.5 per cent and the number of people being admitted to hospital.

She said the same criteria could not be used to take an area out of the highest tier because there is very little chance they can meet it in the four-week review period.

Dr Gardiner said: "I think it would be important to see a stabilisation of case rates, ideally before coming out of a tier."

How are the decisions going to be made?

Dr Gardiner said the decision to move an area out of the top tier will come after discussions between public health officials and local leaders.

She added: "There's a lot of professional judgment that needs to be brought to bear, looking at those key indicators and trying to understand if there is a stabilisation or slowing of growth so that NHS colleagues are feeling more comfortable about their ability to retain key services."

How long will it take to know if the tier system is working?

Dr Gardiner said it will take two to three weeks to establish whether tough top-tier coronavirus restrictions are working in a region.

She said part of the lag comes from the virus having a 10-day incubation period.