Parents should send primary-age children back to schools which remain open this week, the Prime Minister has said, despite growing calls from unions to close them.
Boris Johnson said he understood concerns about children returning for the new term, but said he has "no doubt" that schools are safe and that education was a "priority".
Despite the reassurances, Mr Johnson did not rule out further school closures in England, warning that a range of tougher coronavirus measures may be needed to curb the spread of the virus.
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 local 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 be shut for the next two weeks.
Appearing on the BBC's Andrew Marr Show on Sunday morning, Mr Johnson said: "Schools are safe. It is very, very important to stress that.
"I would advise all parents thinking about want to do, look at where your area is, overwhelmingly you'll be in a part of the country where primary schools tomorrow will be open."
A further 454 people have died within 28 days of testing positive for Covid-19 as of Sunday, while there were another 54,990 lab-confirmed cases of coronavirus in the UK, according to the Government.
It comes as the NHS ramps up its vaccination programme with the newly approved Oxford University and AstraZeneca jab, with 530,000 doses available for rollout across the UK from Monday.
Six hospital trusts will be the first to administer the vaccine before the bulk of supplies are sent to hundreds of GP-led services to be rolled out, according to NHS England.
Education Secretary Gavin Williamson confirmed on Friday that all of London's primary schools would remain shut to most students, rather than just those in certain boroughs as set out earlier in the week.
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.
General secretary of the National Education Union (NEU) Dr Mary Bousted has said schools should stay closed for two weeks to "break the chain" of transmission and prevent the NHS becoming "overwhelmed".
The union, which represents the majority of teachers, has advised its members it is not safe to return to classrooms on Monday.
NAHT general secretary Paul Whiteman said the union had started preliminary steps in legal proceedings against the Department for Education (DfE), asking it to share its scientific data about safety and transmission rates.
On Sunday, Cumbria County Council said it had written to the department 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.
Elsewhere, leader of Kent County Council Roger Gough urged Mr 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.
In a letter to Education Secretary Gavin Williamson yesterday (Saturday), Kent County Council Leader Roger Gough urged the Secretary of State to keep primary schools closed in Thanet, Canterbury, Dover and Folkestone and Hythe. https://t.co/BhBFJHrfhv
— KCC Press Office (@KCCpressdesk) January 3, 2021
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.
Green Party-led 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.
Professor Sir Mark Walport, a member of the Scientific Advisory Group for Emergencies (Sage), warned that it would be difficult to keep the new variant under control without "much tighter" social distancing measures.
Asked if this meant closing schools, the former chief scientific adviser told the Andrew Marr Show that a person aged between 12 and 16 is "seven times more likely than others in a household to bring the infection into a household".
Meanwhile, the latest NHS data revealed that the number of hospital beds in England occupied by confirmed coronavirus patients climbed by 33% between Christmas Day and January 2.
Chris Hopson, chief executive of NHS Providers, told Sky News this increase was the equivalent of "12 extra full hospitals, full of Covid patients" in just eight days.
"So you can imagine why people in the NHS are worried about how quickly this virus is spreading," he added.
In Wales, schools are set to use staggered returns for pupils with face-to-face learning expected to return for most by January 11 and a full return before January 18.
Elsewhere, First Minister Arlene Foster said remote learning for school children in Northern Ireland should only be for a short period.
Primary pupils are to be taught remotely for the week from January 4-8, while for secondary school Years 8 to 11, remote learning is due to last for the entire month.
In Scotland, Nicola Sturgeon said the "planning assumption" remains to open schools on January 18, but parents will be informed of any changes that may be necessary.