The UK’s four chief medical officers have lowered the country’s Covid-19 alert level from four to three after a “steady decrease” in cases.

It comes weeks after the Government defended easing lockdown restrictions in England before the country’s coronavirus alert level had been reduced.

But what is the alert system and how does it work?

– What is the alert system?

The Covid Alert Levels system was announced by Prime Minister Boris Johnson in his televised address to the nation on May 10.

The system is similar to that used to establish the terrorist threat and run by a new Joint Biosecurity Centre.

It has five tiers from level one to five based on the spread of Covid-19 through the country.

– How does it work?

Mr Johnson said that the country’s alert level would be determined primarily by the virus’ reproduction rate – the average number of people that will contract coronavirus from an infected person – and the number of coronavirus cases.

The level then informs the Government what measures are needed to combat the spread of the virus, with higher levels requiring stricter controls.

– What are the different levels?

When the scheme was launched, the country was at level four, which means a “Covid-19 epidemic is in general circulation, transmission is high or rising exponentially”.

The system says that current social distancing measures and restrictions should remain in place.

Level five is when transmission is high or rising but also when there was a risk of healthcare services being overwhelmed and will require an increase in social distancing measures.

Level one means Covid-19 is no longer known to be in the UK and the only action should be “routine international monitoring”.

Level three is when the epidemic is in general circulation and gradual easing of restrictions can take place, while level two is when the number of cases and transmission is low and “no or minimal” restrictions are required.

But under level two there will be enhanced testing, tracing, monitoring and screening.

– What does downgrading the alert level mean to easing lockdown?

Government guidance states that a reduction of the alert level three will mean the “gradual relaxing of restrictions and social distancing measures”.

Representatives from industries, such as the hospitality sector, may hope it could also pave the way for the two-metre rule to be relaxed which is key for many pubs, restaurants and cafes to reopen.

Prof Matt Keeling, of Warwick University, believes the downgrade is currently “justified” but cautions against the easing of social distancing.

He said: “The move to level three is not a time for complacency, there is still the prospect of a second wave if controls are relaxed too quickly and the reproductive number (R) rises above one.

“We are likely to be entering a new phase of this outbreak, where nationally and regionally cases will continue to decline, but locally there will be isolated clusters of cases that need to be contained.”

– Who monitors and sets the level?

Mr Johnson established a new Joint Biosecurity Centre to run the alert system.

Cabinet Office documents said that the centre would provide real-time analysis and assessment of Covid-19 outbreaks at a community level to enable rapid action to stop spikes in infection.

It also advises on specific actions which can be taken to manage rising numbers of infections, such as closing schools or businesses.

The centre also informs the chief medical officers of a change in the Covid-19 Alert level who will then advise ministers.