Video report by ITV News Political Correspondent Paul Brand
Boris Johnson is resisting pressure to announce a blanket closure of all schools in England, despite growing concerns about rising Covid-19 rates across the country, and two new fast-spreading variants of the virus.
The prime minister said there is "no question" that tougher coronavirus measures will be needed to bring levels down, hinting at further national restrictions, but closing primary schools is the "last resort".
He said the argument for keeping schools open was "very powerful" and one of the things he looks back on with the greatest misgivings was closing primary schools in the first wave of the pandemic.
But education unions, local authorities and teachers have called on the government to close all schools for a brief period so the impact of the new Covid-19 variants on teachers and class rooms can be assessed.
Unions including the National Association of Head Teachers, the National Education Union (NEU), the NASUWT teachers' union, GMB, Unison and Unite, in a joint statement, said bringing all schools back at once would put teachers at "serious risk" of falling ill.
Reduced staffing numbers and the safety of vulnerable students is said to be causing "confusion and stress" among school staff, with teachers voicing concerns over balancing support for pupils and the risk to their own health.
Year 4 teacher Tom Dalton told the PA news agency: "You hear so many things, and the fact this new strain is so much more transmittable from children, which immediately rings alarm bells that school is not a safe place to be because you have got 30 children in a quite confined space.
"If I'm wearing my teaching hat I am thinking, we have got to deliver the best quality education we can for these children. However, if I am thinking more from a selfish personal point of view, it's really worrying being here.
"It doesn't feel safe being here."
Prime Minister Johnson insisted the risk to teachers was "no greater than it is to anyone else".
All of London’s primary schools and those in some surrounding areas will not reopen until January 18 due to the fast-spreading variant of Covid-19, with students elsewhere expected to return to classrooms on Monday.
But councils in Cumbria and Kent have urged the government to allow schools to remain closed in other areas, while teaching unions are calling for all schools to switch to remote learning for a brief period.
Secondary schools in England will reopen on a staggered basis, with exam year pupils returning on January 11 and others returning a week later.
All schools will remain open for vulnerable pupils and the children of key workers, as they did when they were shut in the spring and early summer.
In Scotland, the Christmas holidays have been extended to January 11, and the following week will be online learning only. A full return to face-to-face learning is planned for January 18.
In Northern Ireland, primary school pupils will be taught online until January 11. In secondary schools, years 8 to 11 will be taught online throughout January. Years 12 to 14 will return to school after the first week of January.
In Wales, local councils have been told they can be "flexible" with when they open - with many schools aiming to return for face-to-face lessons from January 11.
Prime Minister Johnson, on Sunday, said he has “no doubt” that classrooms are safe and parents should send children back to schools in England which remain open.
A number of primary schools in Tier 4 Co Durham said they would not be opening after the county council told schools decisions should be made by leaders and governors “based on individual risk assessments at local level”.
Paul Whiteman, general secretary of school leaders’ union NAHT, said it was “very hard to tell” how many schools would be open for the start of the term.
“Some schools in Tier 4 areas will be open for vulnerable pupils and key worker families and will be providing remote learning for others, yet in other areas also in Tier 4, all pupils will be admitted,” he said.
“That’s a confusing picture for school leaders and families alike.”
Health Secretary Matt Hancock said primary schools would only close as a "last resort", but the "necessity to keep the virus under control" meant the government was forced to close some education settings.
He added: "We keep all these lockdown-type measures under review, of course we do, and we've shown that we're willing to move quickly if necessary, in order to keep people safe whilst we get the vaccine rolled out."
On Sunday, Cumbria County Council said it had written to the Department for Education (DfE) for permission to keep primary schools in the area closed for the first two weeks of term.
Stewart Young, leader of the council in the rural county – which is one of the areas outside London and the South East hardest hit by the variant, said the Government had responded that schools should open as planned.
“This is disappointing news and I feel that this is the wrong decision for Cumbria and for our families and communities,” he said in a statement.
Leader of Kent County Council Roger Gough urged Education Secretary Gavin Williamson to keep all primary schools in the county closed, saying it is “very hard to justify” letting some schools open while others are closed.
Primary school pupils in Thanet, Canterbury, Dover and Folkestone and Hythe are expected to return on Monday while the other districts in Kent will learn remotely for the first two weeks of term.
Similarly, Essex County Council said it was seeking “urgent clarity” from the Government on the position of reopening schools in north Essex amid rising infection rates.
It said that primary schools in Colchester, Tendring and Uttlesford – the only districts in Essex where schools were due to reopen – would move to remote learning from Tuesday.
Brighton and Hove City Council has advised primary schools in the Tier 4 area not to return in person, except for vulnerable children and those of key workers, until January 18.
Secondary schools in England will have a staggered return, with those taking exams this year resuming in-person teaching on January 11 and other year groups on January 18.
Labour is urging the government to implement a fresh national lockdown, in a bid to bring down virus transmission, but says schools should be the last to close.
Shadow education secretary Kate Green told ITV News the party wants "an immediate national lockdown, to try to get on top of the virus".
She said non-essential businesses which are open in Tier 3 areas, such as zoos, should close before pupils are told to stay away from school.
"Keeping schools open should be the top priority, we don't want to see primary schools closed," she said.
She added: "We think that measures now to control the spread of the virus in the community with a more stringent lockdown give a better chance of keeping our schools open and giving priority to children and young people's learning."