The Government is facing increasing pressure from teaching unions to delay the reopening of all schools in England amid fears over the spread of the new strain of Covid-19.
The National Education Union (NEU) said all primary and secondary schools should remain closed for two weeks following the Christmas break, while the NASUWT has written to the Education Secretary calling for an "immediate nationwide move to remote education" for all pupils.
On Friday, Gavin Williamson confirmed that all London primary schools will remain shut next week – rather than just those in certain boroughs as set out earlier in the week.
But unions say extending that to all schools in England is "the only sensible and credible option".
General secretary of the NEU, Dr Mary Bousted, told BBC Breakfast: "The danger is that by opening schools as levels of infection are rising so high and are already so high amongst pupils, then we're not going to break that chain and our NHS will become overwhelmed so we said all schools should be closed for the first two weeks.
"We regret to have to say that, we don't want to have to say the schools will close but our fear is if we don't do something now, they're going to have to be closed for a much longer period later on this month."
NASUWT general secretary Patrick Roach said it was "now abundantly clear" that the pandemic was impacting on the ability of schools to operate normally.
"There is genuine concern that schools and colleges are not able to reopen fully and safely at this time," he said.
"The NASUWT remains of the view that schools, colleges and other settings should only remain open to all pupils where it is safe for them to do so."
The National Association of Head Teachers (NAHT) called for the Government to move all schools to home learning for a "brief and determined period for most children", adding that the new strain had created "intolerable risk" to schools, while the GMB union, which represents school support workers, said a consistent approach was needed, rather than "a postcode lottery".
Mr Williamson had said the decision to close all London primary schools was a "last resort".
We must #MakeSchoolsSafe so we can #protectcommunities. Members please register for our emergency briefings and tomorrow's will be live streamed on social media. We will be announcing the decision of the Executive later. pic.twitter.com/Dmim5YxvoX
— National Education Union (@NEUnion) January 2, 2021
From January 4, London primary schools will be required to provide remote learning for two weeks to all children except vulnerable children and those of key workers, who will be permitted to continue to attend.
Under the Government's initial plan, secondary schools and colleges were set to be closed to most pupils for the first two weeks of January, while primary schools within 50 local authorities in London and the south of England were also told to keep their doors shut until January 18.
Professor Russell Viner, president of the Royal College of Paediatrics and Child Health, has previously said schools "should be the last places to close" and called for an "ambitious, national and properly funded recovery plan" for children and young people which he described as "especially vital" if schools remain partially or fully closed in the early part of the year.
Scientific Advisory Group for Emergencies (Sage) member Dr Mike Tildesley told the BBC on Saturday that the evidence was "that we are not getting a significant increase in cases in a primary school setting despite this new variant".
The school row comes after figures showed a further 53,285 lab-confirmed cases of coronavirus in the UK as of 9am on Friday, with another 613 deaths within 28 days of a positive test.
This was the fourth day in a row daily cases have been above 50,000, with a new record high of 55,892 cases reported on New Year's Eve – the highest since mass testing began in late May.
Professor Andrew Goddard, president of the Royal College of Physicians, said the current case figures are "fairly mild" compared to what is expected in a week's time and that healthcare workers are "really worried" about the coming months, with infection levels putting hospitals under increasing pressure.
He told the BBC: "All hospitals that haven't had the big pressures that they've had in the South East, and London and South Wales, should expect that it's going to come their way.
"This new variant is definitely more infectious and is spreading across the whole of the country. It seems very likely that we are going to see more and more cases, wherever people work in the UK, and we need to be prepared for that."
One nurse described the situation in hospitals as "unbearable".
The nurse, who works at the Whittington Hospital in north London, described patients being left in corridors, some spending up to three hours in ambulances because of a lack of beds and one being left without oxygen when their cylinder ran out.
Meanwhile, the UK is preparing to send out the new Oxford University and AstraZeneca vaccine, with 530,000 doses available for rollout from Monday.
The Times reported that a member of the Oxford/AstraZeneca team had said two million doses of the Oxford vaccine are due to be supplied each week by the middle of January.
Rollout of the Pfizer/BioNTech jab began almost a month ago but second doses of either vaccine will now take place within 12 weeks rather than 21 days as initially planned.
Deputy chairman of the Joint Committee on Vaccination and Immunisation (JCVI), Professor Anthony Harnden, defended the plans.
He told BBC Radio 4's Today programme on Saturday that patients he had dealt with accepted the move, stating: "When it was explained to them that the vaccine offers 90% protection for one dose, and the priority was to get as many people vaccinated in the elderly and vulnerable community as possible, they understood.
"I think the country is all in this together.
"And, I think we really, really want to pull together to try and do the best strategy possible."