Boris Johnson insisted the risk to teachers was no greater than to anyone else as the Government came under pressure to keep the majority of pupils out of class and to switch to remote education.

The Prime Minister said the argument for keeping schools open was “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.

His comments came as a coalition of education unions warned that bringing all pupils back to school could fuel the pandemic and put teachers at “serious risk” of falling ill amid the new variant of Covid-19.

The Government’s “chaotic” handling of the opening of schools has caused confusion for parents and teachers, according to a joint statement from unions representing school staff and headteachers.

All of London’s primary schools and those in some surrounding areas worst hit by Covid-19 will not reopen until January 18, with students elsewhere in England expected to return to class this week.

Mr Johnson has insisted that schools are safe as he said that closing primary schools was a “last resort”.

The Prime Minister said: “The risk to teachers, and of course we will do everything we can to protect teachers, but the risk to teachers is no greater than it is to anyone else.

“The reasons for wanting to keep schools open I think are very, very powerful.”

It came as the Conservative former health secretary Jeremy Hunt called for the closure of schools “right away” as he warned that the pressures facing hospitals are “off-the-scale worse” than previous winter crises.

Early findings from a small study carried out in November suggested that the proportion of schoolchildren and teachers with coronavirus mirrors the proportion in the local community.

The study of 105 schools, published by the Office for National Statistics (ONS) last month, found that 1.24% of pupils and 1.29% of staff overall tested positive for current infection – similar to the 1.2% reported in the community.

But no data or major study has been published since the new strain of coronavirus came to light.

The NAHT school leaders’ union is calling on the Government to disclose scientific evidence regarding the impact of the new Covid-19 variant on schools.

NAHT general secretary Paul Whiteman said: “NAHT began legal proceedings last Friday to force the government to reveal the scientific data it is withholding that underpin its assertions that schools are safe. We remain unconvinced, and we await the Government’s reply, which is due at 4pm today.”

The NAHT – alongside the National Education Union (NEU), the NASUWT teachers’ union, GMB, Unison and Unite – have called for a move to remote learning for most pupils amid safety concerns.

All staff continuing to work in schools with vulnerable pupils and children of key workers should be given priority access to Covid-19 vaccinations, the coalition of unions adds.

A joint statement says: “Bringing all pupils back into classrooms while the rate of infection is so high is exposing education sector workers to serious risk of ill-health and could fuel the pandemic.”

The education unions are calling on the Prime Minister to order a “pause” in a return to the classroom until the safety of staff and pupils can be guaranteed.

They say Boris Johnson should sit down with unions to “discuss a joint approach” to ensure schools are safe, and pupils have the equipment they need to receive remote learning.

It comes after the NEU advised its members that it is not safe to return to classrooms on Monday.

Gildersome Primary School in Leeds, which is in Tier 3, has been forced to shut to most children indefinitely after 16 staff signed a letter saying they are “exercising their right not to teach full classes”.

But Health Secretary Matt Hancock told Sky News that it is “clear that the proportion of teachers who catch coronavirus is no higher than the rest of the population”.

He added: “So there is clear public health advice behind the position that we have taken and that is what people should follow because, of course, education is very important as well, especially for people’s long-term health.”

Secondary schools and colleges 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.

Testing kits are being sent out to secondary schools and colleges this week in preparation for the mass testing of pupils when they return to class.

But confusion remains among teachers and parents about school closures following last-minute Government announcements over the Christmas holidays about the delayed reopening of some schools.

And a number of councils – including Cumbria and Kent – have urged the Government to allow all primary schools in their areas to remain closed.

Bryony Baynes, head of Kempsey Primary School in Worcestershire, said she feels “frustrated” at the lack of clear leadership over the issue.

She told the PA news agency: “I feel sick with anxiety. I emailed all my staff last night because I am aware that the NEU has issued guidance letters and all of my staff are committed to being in school.

“They are, as I am, very anxious, but are determined to do their best for the children in our care.”

Ms Baynes added: “I have to depend on the DfE (Department for Education) and my local authority to lead me and, at the moment, I don’t feel that leadership is clear.”

One parent, who asked to remain anonymous, said she would not be sending her children to school due to her coronavirus safety concerns.

As she has severe asthma, the woman told PA she could not risk her children bringing the virus home so she would be teaching them herself.

She said: “We have all managed to avoid catching Covid so far, but with this new strain, I don’t think it’s safe at all.”