Britain is facing a "very dangerous moment" with the easing of lockdown restrictions, says the deputy chief medical officer Professor Jonathan Van-Tam.
From Monday, in England up to six people will be allowed to meet outside in parks and gardens if social distancing of two metres is observed.
Downing Street has warned the public that these meet-ups remain prohibited until after the weekend.
On Saturday, people flocked to beaches and beauty spots in the warm weather.
In England, some pupils are due to go back to school next week, and markets and car showrooms will be open. Non-essential shops are set to start trading again in mid-June.
England's deputy CMO Professor Van-Tam called for people to show restraint, saying the government and the public had a "dual responsibility" to prevent a second wave of the coronavirus.
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Speaking at the Number 10 briefing, he added: "I believe this is also a very dangerous moment. We have to get this right."
Three members of the Scientific Advisory Group for Emergencies (SAGE) – Professor John Edmunds, Sir Jeremy Farrar and Professor Peter Horby – have warned ministers are taking risks, with around 8,000 people daily thought to be catching coronavirus in England, and that does not include hospitals or care homes.
The scientists have expressed concern that the NHS test and trace system to help stop the spread of COVID-19 is yet to be proven to be working effectively, and the reproduction rate of the virus is still only just below one.
This "R" number is the measure of how many people will be infected for every one person who has the disease.
Professor Edmunds told Sky News: "Small changes can put that reproduction number up above one. The more important thing is that we still have a lot of cases."
Sir Jeremy said in a Twitter post: "COVID-19 spreading too fast to lift lockdown in England. Agree with John and clear science advice.
"TTI (test, trace and isolate) has to be in place, fully working, capable dealing any surge immediately, locally responsive, rapid results & infection rates have to be lower. And trusted."
Professor Van-Tam said scientific opinions "always vary to some extent", and told the news conference the lockdown easing must go "painstakingly" slowly.
He urged the public to follow the guidance, adding: "Don't tear the pants out of it, and don't go further than the guidance actually says."
Meanwhile, Professor Van-Tam was asked about comments that Professor Edmunds had given to Sky News that "the government are pretending they're not makRead More – Source