Masks are returning to classrooms and plans are being drawn up for possible absence levels of up to a quarter of public sector workers as Omicron continues to spread across the country.

The moves come after a health boss warned the “next few days are crucial” in the fight to reduce the impact of the highly transmissible coronavirus variant, as NHS staff work “flat out”.

Education Secretary Nadhim Zahawi acknowledged the variant “presents challenges”, but said the government is taking steps to “bolster our support for schools” in an effort to minimise disruption when pupils return to their desks after the Christmas break.

Face coverings will return for secondary school pupils in England – having already been recommended in communal areas for older students and staff.

But the supply of 7,000 new air purifiers for areas of schools where good ventilation is difficult has been branded “completely inadequate” by NEU teaching union joint general secretary Dr Mary Bousted.

She said that with “over 300,000 classrooms in England they (the government) have failed to provide an effective solution”.

Education committee chairman Robert Halfon said mask-wearing would have a “significant impact on children’s wellbeing”.

In comments in the Sunday Telegraph, the Tory MP said: “The government needs to supply the evidence.

"If masks are not required in offices or restaurants, why are we getting young kids to put them on?”

His colleague Mr Zahawi, writing in the same paper, said it was his “firm belief that, despite the bumps in the road that inevitably occur with a virus of this nature, we are transitioning from pandemic to endemic in this country”.

“That does not mean that we can take our eye of the ball or that we can throw caution to the wind," he added.

"But it does mean that there can be no excuse for our children not learning face to face in the classroom where they want and need to be."

'We’re rather disappointed that we’re having the conversations this side of Christmas when we could have been making these arrangements earlier on.'

Paul Whiteman, general secretary of school leaders’ union NAHT, said ministers should have acted sooner.

“We are really pleased that government is talking to us and trying to work out how to get some support into schools now,” Mr Whiteman told the BBC.

“We’re rather disappointed that we’re having the conversations this side of Christmas when we could have been making these arrangements earlier on.

“The other thing we’re going to need is a very flexible approach from government that means as we begin to understand the picture more and more, they’re prepared to make other changes very quickly.”

Meanwhile, the Cabinet Office said that although disruption caused by Omicron has so far been controlled in “most parts of the public sector”, leaders have been asked to test plans against “worst case scenarios” of 10%, 20% and 25% workforce absence rates.

It follows a call in December from Mr Zahawi for ex-teachers to help with Covid-related staff shortages in the new year.

Boris Johnson has tasked ministers with developing “robust contingency plans” for workplace absences as the government acknowledged high Covid levels could hit businesses hard over the coming weeks.

As the rollout of boosters continues, Health Secretary Sajid Javid hailed the delivery of 132 million vaccinations across the UK throughout 2021 as “astounding and a true reflection of the fantastic work of our NHS and its volunteers”.

Mr Javid has warned that restrictions on freedom “must be an absolute last resort”, but on Saturday NHS Providers chief executive Chris Hopson said the government “must be ready to introduce new restrictions at pace if they’re needed”.

The most recent rules are set to expire six weeks after implementation, with a review after three weeks, which is expected on or close to Tuesday, January 4.

A further 162,572 lab-confirmed Covid-19 cases were recorded in England as of 9am on Saturday, a new record for daily reported cases in the nation.