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Scientific evidence for reopening England’s schools on June 1 will finally be made public on Friday, Downing Street has revealed.

In a move long demanded by teachers, councils and parents, the government’s Scientific Advisory Group on Emergencies (Sage) will publish details of its modelling.

The very latest R number – which sets out how the Covid-19 virus is being spread among the population – will also be updated at the same time, the prime minister’s spokesperson said.

Both sets of facts are seen as key preconditions for the reopening of schools, particularly with teaching and other education unions refusing to engage with the proposals before the science is shared.

Boris Johnson has also insisted that he will not go ahead with further easing of the lockdown if there is a risk that the R number rises above 1, the point at which the virus starts increasing in the community once more.

Scores of councils have warned that they will not allow their local schools to reopen on the June 1 date without being first sure of the safety protections.

Johnson and education secretary Gavin Williamson have said they want some key pupil groups to return to primary schools on that date, beginning with reception classes, Years 1 and 6. 

The PM also said he wanted all primary pupils to return for at least a month’s classroom time before their summer break.

“We are continuing to discuss this with head teachers, teachers and their union representatives. I would expect the Sage evidence on the safety of going back to school to be published later this week,” the PM’s spokesperson said.

“It remains our intention to get as many children as possible back into school as soon as we are able in a way that is safe.”

Scotland’s first minister Nicola Sturgeon announced on Thursday that she wanted her local schools to return after the summer break and not before it.