Schools are being “strongly advised” not to admit more pupils after new data suggested coronavirus could still be spreading in the North West of England.

Headteachers in Tameside, east of Manchester, have been told to delay the wider reopening of schools beyond key workers’ and vulnerable children, planned for Monday, “until there is further assurance,” the council’s director of public health, Dr Jeanelle de Gruchy said in a letter to schools.

The North West has the highest rate of Covid-19 infections in England according to Public Health England (PHE), and data has suggested the reproductive rate, known as the R value, is higher than 1 in the region, a crucial marker for public health.

The R value refers to the average number of people that will contract coronavirus from an infected person.

If it is 1 or higher, the virus will spread exponentially through the population, while a value less than 1 indicates the virus is in decline.

Data from PHE released on Friday gave an R value of 1.01 for the North West and 1.0 for the South West, with all other regions below 1.

Other local councils in the region are understood to be monitoring the situation with Tameside postponing the reopening of schools until June 22.

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 regions and the North not being listened to.

Council bosses in Liverpool and Gateshead led a northern backlash against the Government announcement last month advising schools to reopen for Years 1 and 6 from June 1.

Many councils have instead only partially reopened to pupils other than vulnerable children or those of key workers.

Health Secretary Matt Hancock, speaking at the Downing Street briefing on Friday, said experts on the Scientific Advisory Group for Emergencies (Sage) believe the UK’s overall R number is below 1, but added that local lockdowns would be used when outbreaks are spotted.

He said the PHE data needed to be looked at “in the round” with other data.

Mr Hancock added: “The discussion of the higher R in the North West and the South West that’s estimated compared to the rest of the country is an important part of moving towards a more localised approach rather than a national approach to the lockdown.”

In the letter to headteachers from Dr de Gruchy, she said after initially supporting the gradual reopening of school in Tameside the advice had now changed.

“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,” she said.

Colin Cox, director of public health in Cumbria, also warned on Friday people should not be “complacent” and lockdown restrictions could be tightened if the R number increases.