The UK has lowered its Covid-19 alert level from 4 to 3, meaning transmission of the virus is no longer judged to be “high or exponentially rising”, raising expectations that physical distancing restrictions could be cut. The downgrade, which was endorsed by all four chief medical officers, could pave the way for some physical distancing measures to be eased, but they cautioned that the pandemic was not over. After the lowering of the alert level Boris Johnson said to “watch this space” when asked during a Hertfordshire school visit whether distancing restrictions could be cut to help schools return in September. Whitehall sources suggested that meant the review of the 2-metre rule commissioned by the prime minister could report as soon as next week. Johnson said: “We have to start thinking of a world in which we are less apprehensive about this disease … I hope, as we go forward into the autumn, people will be much, much more confident.” Downing Street is under intense pressure to relax restrictions, with the hospitality industry still unclear what guidance it will have to follow if it reopens as planned on 4 July. Emma McClarkin, the chief executive of the British Beer and Pub Association, said a decision could not come soon enough. “We are disappointed the PM hasn’t answered our desperate plea for urgent clarity. In light of the announcement that the country is moving to covid alert level 3, we’d really hoped we would hear some positive news today.” Johnson’s comments came as documents released on Friday by the UK government’s committee of experts revealed scientists warned ministers that public adherence to physical distancing measures may crumble once it is suggested that lockdown restrictions are set to be lifted. The minutes from a 21 May meeting show the government’s own advisers had deep concerns that easing measures at that stage could result in the country’s test-and-trace system being “very rapidly overwhelmed”. The UK has been at level 4 since the five-tier alert system was announced in May, and the shift to level 3 means Covid-19 is now considered to be “in general circulation”, with the threat level moving from “severe” to “substantial”. The chief medical officers said levels of infection meant there were still likely to be localised outbreaks. The alert level is set by the joint biosecurity centre, based on evidence including the “R”, or reproduction number, and the number of confirmed cases at a given time. The latest government estimates suggest R is hovering just under 1 in most parts of the country and that numbers of cases are slowly declining. In a statement, the chief medical officers said: “The CMOs for England, Scotland, Wales and Northern Ireland have reviewed the evidence and agree with this recommendation to move to level 3 across the UK. “There has been a steady decrease in cases we have seen in all four nations, and this continues. It does not mean that the pandemic is over. The virus is still in general circulation, and localised outbreaks are likely to occur. “We have made progress against the virus thanks to the efforts of the public and we need the public to continue to follow the guidelines carefully to ensure this progress continues.” The health secretary, Matt Hancock, said: “The UK moving to a lower alert level is a big moment for the country, and a real testament to the British people’s determination to beat this virus.” A Downing Street spokesman said the downgrade did not automatically mean a change to lockdown restrictions. “We’ve said throughout that easing the lockdown will be contingent on continuing to meet the five tests, making sure that any changes we make won’t result in the NHS becoming overwhelmed, and the continuation of infections and fatalities being reduced.” Asked if this meant the public should not necessarily expect any changes to existing timetables to ease restrictions, he said: “I would say that it will be used by government to inform decisions on the continuing easing of lockdown. They are not contingent on each other.” Last month, members of the government’s Scientific Advisory Group for Emergencies (Sage) criticised the government for easing restrictions, including allowing groups of six people to meet outdoors and encouraging people to return to work, before the threat level had been reduced. The latest tranche of Sage documents reveal the behind-the-scenes warnings that preceded these public interventions. The scientists advised that the R value could return to 1.7 in a reasonable worst-case scenario of restrictions being eased without a “proven” test-and-trace system in place. The scientists also raised the prospect of test-and-trace capacity being a greater challenge in winter because people spent more time indoors, allowing the virus to spread more easily, and because of the increased number of people with other seasonal illnesses seeking tests. In the first week of test and trace, beginning 28 May, there were 23,000 symptomatic infections in England, according to the Office for National Statistics, but just over 8,000 people who had tested positive were contacted by the tracing teams, and 5,400 of those handed over the phone numbers and email addresses 0f those they had met. The teams managed to reach just under 27,000 people and asked them to self-isolate. Nearly 5,000 more, however, were not reached or refused to comply.