The recommendation comes as the government pledges to keep face-to-face education going despite surging COVID-19 infections in England, with a record 162,572 new cases reported on Saturday.

The government is also drawing up contingency plans over fears a quarter of public sector workers could be absent due to the Omicron wave.

Masks will "maximise the number of children in school" for the "maximum amount of time", said the government, stressing the "temporary" guidance for schools and colleges will be reviewed on 26 January when Plan B regulations are scheduled to expire.

However, senior figures in the education sector are warning that classes and year groups may again have to learn from home due to issues with staffing levels caused by the pandemic.

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The government has said an additional 7,000 air cleaning units are going to be provided to schools, colleges and early years settings ahead of young people returning from the Christmas holidays.

But the NEU teaching union has criticised the number of units as "completely inadequate".

Paul Whiteman, the head of school leaders' union NAHT, welcomed the moves over masks and air filtration systems, and said "the best place for children to learn is in school".

"We need to do everything possible to ensure face-to-face teaching continues, despite increasing infection rates due to the new variant," he said.

Face coverings are already encouraged for secondary school and older students in communal areas and corridors, but the existing guidance does not advise to wear them in classrooms.

Shadow health secretary Wes Streeting said: "If the choice is between having masks at schools or children missing schools in huge numbers, of course we want to keep pupils learning. That's got to be the priority.

"Pupils should be testing twice a week. There's lots of evidence to suggest that hasn't been happening properly. So the message for Government is get the tests in place, make sure pupils are able to test twice a week."

Robert Halfon, conservative MP and chairman of the House of Commons Education Select Committee said: "What I'd like the Government to do is set out why they're doing this, set out the evidence in the House of Commons... I do worry masks in schools will have a negative impact."

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Geoff Barton, the head of the Association of School and College Leaders, also supported the latest moves.

He said: "While there are obvious drawbacks to the use of face coverings in classrooms, it is clear that the Omicron variant poses a very significant additional risk to education with the potential for further widespread disruption of schools, colleges, and young people."

And he warned that as staffing levels were disrupted by the surge in cases, some classes and year groups could be forced to learn from home again.

"All of this is a recognition by the government that the spring term will be extremely challenging for schools and colleges," he added.

What is Plan B?

The government said that on top of a break from Ofsted inspections in the first week of term - which had already been announced - schools are being encouraged to ask for a deferral if they are "significantly impacted by COVID-related staff absence".

It comes as six trade unions for education workers have urged the government to offer improved financial support for schools and colleges to help cover the costs of supply staff.

Also, there has been a nationwide shortage of lateral flow and PCR tests in the UK over recent weeks and schools are being asked to test pupils when they return after the Christmas break.

But a spokesperson for the Department for Education told Sky News that the shortage in lateral flow tests for delivery on the government's portal will not impact tests being provided to schools.

"Schools and colleges use a different priority supply route to get their lateral flow tests," they explained.

"Most test kits have already been received for the start of the new term and we have arrangements in place to make sure every school has the testing it needs."