Up to one-in-five teachers are self-isolating and the figure is rapidly rising in response to the coronavirus emergency, school leaders have said.

Geoff Barton, the general secretary of the Association of School and College Leaders, said that typically between 10 and 20 per cent of teachers are self-isolating in response to the outbreak.

He warned that this, coupled with falling pupil attendance - which he said was currently around 70 to 80 per cent - meant it was increasingly difficult to keep schools open.

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He said: “We don’t have definitive data on the proportion of teachers who are self-isolating, but we are typically hearing that it is between 10 per cent to 20 per cent, and that this number is rapidly rising.

“It’s our understanding that some schools are already instigating a partial closure today and foresee this extending further tomorrow.

“Attendance at school is also falling and is typically running at between 70 per cent and 80 per cent. This is also likely to become worse as the situation develops.

“It is clearly becoming increasingly difficult to keep schools open and we now urgently need some clear strategic planning from the government.

“The priorities must be how we continue to support pupils whose parents are key workers, and those in vulnerable groups, such as children who receive free school meals.

“Simply expecting all schools to remain open is becoming increasingly untenable and will end up being counter-productive because closures will happen without coordination.”

Mr Barton and the general secretary of the NAHT school leaders’ union Paul Whiteman warned that it would be more difficult to keep schools open as a result of staff absences after meeting education secretary Gavin Williamson for talks yesterday.