Watch: What are the four stages of easing coronavirus restrictions?
England's chief medical officer has explained why there is a five-week gap between each stage of the lifting of coronavirus restrictions announced in Boris Johnson's roadmap.
Professor Chris Whitty said the gap was necessary to look at the effect of each period of 'opening up' and see whether it was in line with expectations or worse.
On Monday, the government released its roadmap for the easing of restrictions in England, starting with the return to schools on 8 March, and moving to the second stage involving hairdressers, shops, gyms and outdoor hospitality on 12 April, indoor socialising and hospitality on 17 May, then all legal limits on social contact lifted on 21 June.
Explaining why a five-week gap had been decided between the four stages of the roadmap at a press conference on Monday evening, Whitty said: "The reason for that is that inevitably for each one of these steps we are taking a risk which is an accepted risk.
"There is a risk to this and everybody in the country I'm sure understands this.
"What we want to do is after each set of risks with a particular set of opening up, wait until we have data that tells us 'has this done what we expected it to, have we actually ended up in a slightly worse place than we thought we would, or have indeed we ended up in a slightly better place?'
"But I think the big worry is have things got slightly worse than we were expecting?
"We cannot measure that in less than about four weeks because it takes that long for the effect to be seen and the data to come through and be analysed.
"So that's the reason for the five-week gap because it allows us to see whether it's had an effect and then to make a judgment as to whether that's material on making the next decision. That's the basis on which this is done."
The government has said that the five-week period will allow it to analyse the impact of the new restrictions and then to give the country a week's notice if there are any changes to the planned roadmap.
Announcing his roadmap, the prime minister said the government aims to have "removed all legal limits on social contact": including on weddings and other life events, opening the final closed sectors of the economy such as nightclubs, and lifting restrictions on large events and performances by 21 June.
Johnson warned that "we cannot escape the fact that lifting lockdown will result in more cases, more hospitalisations and sadly, more deaths", adding "there will always be some vulnerable people who are not protected by the vaccine".
But he then said: "We cannot persist indefinitely with restrictions that debilitate our economy, our physical and mental wellbeing, and the life chances of our children."
Watch: What UK government COVID-19 support is available?