The UK government is setting up a new alert system is being established to monitor the threat posed by the novel coronavirus.
The Covid-19 monitoring system, similar to that used to establish the terrorist threat, will be run by a new Joint Biosecurity Centre.
The UK is currently at level four of the five-tier system, just below the "most critical" threat - the kind that would have seen the NHS swamped by coronavirus cases.
Boris Johnson used his address to the nation to suggest the country was now edging towards level three.
Follow live updates and reaction from the Prime Minister's speech on our dedicated blog.
You can see how England's lockdown rules now differ from those in Wales here.
The further down the Covid alert level ladder the UK goes, the more lockdown measures could be eased.
The Prime Minister said: "We are establishing a new Covid alert system run by a new Joint Biosecurity Centre.
"And that Covid alert level will be determined primarily by R and the number of coronavirus cases.
"And in turn that Covid alert level will tell us how tough we have to be in our social-distancing measures - the lower the level, the fewer the measures.
"The higher the level, the tougher and stricter we will have to be."
Mr Johnson added: "There will be five alert levels.
"Level one means the disease is no longer present in the UK and level five is the most critical - the kind of situation we could have had if the NHS had been overwhelmed.
"Over the period of the lockdown, we have been in level four, and it is thanks to your sacrifice we are now in a position to begin to move in steps to level three."
