It is not safe for schools to open on 1 June, leading scientists have warned.
A report by the "Independent Sage" committee, chaired by former chief scientific adviser Sir David King, warns that the government's own modelling of school openings shows the R value rising above 1.
It says: "The most recent estimates for the UK are that R is between 0.7-1, meaning that all scenarios modelled by Sage are at risk of pushing R above 1.
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"The school reopening scenario chosen by the government is not one of those modelled by Sage, making the potential impact of reopening even more uncertain."
The report claims the government is failing to follow the advice of its own Sage committee in opening schools on Monday.
It says that analysis by both Sage and Independent Sage means that it is not safe for schools to reopen on 1 June.
"Robust testing systems are not in place everywhere," the report says.
"Additionally, public adherence to social distancing is influenced by trust in the government and its messaging. This trust is increasingly strained.
"We therefore believe that by going ahead with a general school reopening from 1 June, the government is not following the advice of its Sage group and is risking a new surge in cases of Covid-19 in some communities."
It adds: "We believe that decisions on school opening should be guided by evidence that there are low levels of Covid-19 infections in the local community in which the school is situated and the ability to rapidly respond to new infections through a well-functioning, coordinated, local test, track and isolate strategy.
"We have seen no compelling evidence that these conditions have so far been met across the country. Until they are, it is not safe to open schools everywhere on 1 June."
A Department for Education spokesperson said: "We want children back in schools as soon as possible because being with their teachers and friends is so important for their education and their wellbeing.
"Plans for a cautious, phased return of some year groups from 1 June, at the earliest, are based on the best scientific and medical advice. The welfare of children and staff has been at the heart of all decision making.
"We have engaged closely with a range of relevant organisations, including the unions, throughout the past ten weeks, including organising for them to hear directly from the government’s scientific advisers, and will continue to do so.
"We have also published detailed guidance on the protective measures schools should take to reduce the risk of transmission."