Schools are being “strongly advised” not to admit more pupils after new data suggested coronavirus could still be spreading in North West England.
Headteachers in Tameside, east of Manchester, have been ordered to delay the wider reopening of schools beyond key workers’ and vulnerable children, planned for Monday, until at least June 22.
Public Health England (PHE) analysis with Cambridge University has found that the North West now has an R value - the reproduction rate of the virus - of 1.01, the highest in Britain.
When the R is above 1, the virus resumes rapid contagion.
The revelation on Friday prompted Tameside council’s director of public health, Dr Jeanelle de Gruchy, to tell schools they should halt reopening “until there is further assurance”.
The council had given the green light for nursery, reception and Years 1 and 6 to return from Monday in line with Boris Johnson's push to reopen primaries this month.
But Dr Gruchy told school leaders: “Because of this change in R, and despite the excellent work undertaken, I am therefore strongly advising all schools and childcare settings to delay wider opening until at least 22 June for us to be more assured that the rate of infection is reducing and R is firmly below 1.”
Bury Council in Manchester has also written to headteachers suggesting they “reconsider” any plans to reopen to more pupils after the weekend and other authorities in the region are understood to be monitoring the situation.
The Government has suggested a strategy of “local lockdown” measures being introduced to fight any flare-up of the virus in particular areas.
But Andy Burnham, Mayor of Greater Manchester, has questioned whether such measures are workable, calling them a “recipe for chaos”.
Both he and Liverpool City Region Metro Mayor Steve Rotheram have questioned whether lockdown relaxation was being lifted too soon, driven from London, with the concerns of the North not being heard.
Many councils have instead only partially reopened to pupils so far and uncertainty still remains over the Government's June 15 date for reopening secondaries to Year 10 and Year 12 pupils.
Health Secretary Matt Hancock said experts on the Scientific Advisory Group for Emergencies (Sage) believe the UK’s overall R number is below 1, but said local lockdowns would be used when outbreaks are spotted.
It came as a new study by researchers at UCL and the London School of Hygiene and Tropical Medicine said sending all children back in September - even with a phased approach until then - could trigger a second wave in December double the size of April’s peak.
The experts said a contact tracing system more advanced than the current one would need to be in place to prevent this.