The Government has demanded that schools stay open until the end of term as council leaders and headteachers have called for a move to online learning amid a rise in coronavirus cases.
Downing Street has said it expects schools and colleges to remain fully open until the end of Thursday.
It comes after council leaders in England have advised schools in Islington and Greenwich to close early this week and switch to remote learning amid rising Covid-19 rates.
In Basildon in Essex, nearly all the secondary schools have moved to full remote education.
London mayor Sadiq Khan has called on the Government to consider closing all secondary schools and colleges in London early and reopen later in January due to “outbreaks” among 10 to 19-year-olds.
But the Prime Minister’s official spokesman said: “We’ve consistently said that not being in school has a detrimental impact on children’s learning as well as their own personal development and mental health.
“Which is why we expect all schools and colleges to remain open until the end of term on Thursday, as schools have remained open throughout the pandemic.”
Asked whether action will be taken against councils that shut early, the spokesman said: “Our regional school commissioner teams are working closely with schools and local authorities across the country and will continue to work with them and support them to remain open.”
The Department for Education (DfE) has written to all Greenwich and Islington schools in light of the statements from their council leaders.
The regional schools commissioner who oversees Greenwich has sent a letter to the council urging it to U-turn on its position.
It says: “As you will be aware under schedule 17 of the Coronavirus Act 2020, the Secretary of State may make a direction to require schools to enable all pupils to attend full time, other than pupils who are required to self-isolate in accordance with the schools’ opening guidance.
“The Department would consider issuing such a direction, if needed. I would ask that you reconsider your position immediately and retract your message to schools.”
Labour leader Sir Keir Starmer has also urged leaders to try to keep schools open during the last week of term as he said closures are “difficult” for vulnerable children and they can leave parents in the lurch.
But Islington Council is advising schools in the north London borough to shut from Tuesday evening – except for children of key workers and vulnerable pupils – and not to reopen until January 11.
It comes after schools in Greenwich, south-east London, were advised to close from Monday night and switch to remote learning amid a rise in coronavirus cases.
Islington Council leader Richard Watts said: “We must all take action now to stop this deadly disease spreading serious illness and death to the people we love.”
In a statement on Monday, a spokesman for Conservative-run Essex County Council (ECC) said: “As of today, eight of the nine secondary schools in Basildon district are operating a full remote education offer.
“17 primary schools, out of 48 in the Basildon district, have now moved to a full remote education offer.”
But he added: “No school is closed, all the schools are offering a full or partial remote education offer.”
Sir Keir told his LBC radio phone-in: “I’m very reluctant to close our schools down. I’m worried about closing schools early but equally I can see council leaders are put in a difficult situation now.”
Asked what he would say to the London mayor, the Labour leader said: “Talk to the Health Secretary about what we can do this week to keep schools open, try to keep them open this week.”
Schools in England have been told that they can take an inset day on Friday so staff can have a “proper break” from identifying potential Covid-19 cases.
But headteachers have been calling for more flexibility to end in-person teaching earlier to reduce the risk of pupils and staff having to isolate over Christmas.
New powers introduced through the Coronavirus Act allow the Government to issue “directions” to heads around education provision during the pandemic.
But, should schools fail to comply with directions to remain open, Education Secretary Gavin Williamson could apply for a High Court injunction forcing them to do so.
Kevin Courtney, joint general secretary of the National Education Union (NEU), has urged other councils to “take the same decision” as Greenwich Council.
He said: “The Government should have been planning for this weeks ago. They have now started to recognise the blindingly obvious fact that transmission is happening in schools and that this can spread to families. Much more is needed to control the virus in schools and to protect communities.”
Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said: “It is deeply unfair on school leaders, teachers, families and pupils that they are caught between the heavy-handed approach of central government and increasing alarm at local infection rates.”
He added: “Although it is now incredibly late in the day, the Government must remove the threat of legal action and allow schools to make the decisions they need to make on behalf of their staff and children.
“In the future, it must allow for more nuanced responses to local infection rates and the huge disruption affecting many schools rather than insisting on a one-size-fits-all approach.”
A DfE spokeswoman said: “It is a national priority to keep education settings open full time and it is vital that children remain in school until the end of the term.
“Schools, colleges and early years settings across the country have worked tremendously hard to put protective measures in place that are helping reduce the risk of the virus being transmitted and our regional school commissioner teams continue to support local authorities and school trusts to remain open and help resolve any operational issues.”