All pupils in secondary schools in England should return to wearing masks in classrooms, ministers said last night, as fears grew that the new term could trigger a huge spike in cases of the Omicron variant.

The new advice came amid mounting criticism of the government for failing to ensure availability of Covid testing kits in time for the return to schools and workplaces following the Christmas holidays.

The Department for Education said the advice was “short-term only to support pupils and teachers as they return to schools this term” and would remain in place until 26 January, when it would be reviewed.

However, there are mounting concerns among scientists and in the medical profession that a further rapid rise in infections is possible, particularly in England, where rules on socialising over Christmas and the new year were more relaxed .

Yesterday, the number of confirmed cases in England was a record 162,572 . A lack of testing equipment is also adding to staffing problems across public services. All state schools have been asked by the government to carry out on-site testing of pupils before lessons begin this week.

As ministers desperately tried to avoid sparking a new mood of national crisis with school closures, the education secretary Nadhim Zahawi also announced that 7,000 more air cleaning units would be provided to schools and colleges to improve ventilation in classrooms.

In addition many Ofsted school inspections are to be delayed in the first weeks of the new term.

With Boris Johnson under renewed pressure over the handling of the pandemic, Zahawi said everything was being done to ensure the education of young people did not suffer again.

“The prime minister and I have been clear that education is our number one priority,” he said. “These measures will bolster our support for schools as we do everything in our power to minimise disruption.”

The Labour leader Keir Starmer told the Observer that the government’s failure to shore up supplies of tests in response to Omicron’s emergence in November was “unforgivable”.

Starmer said parents should be testing their children at least twice a week to ensure they did not spread the disease to the older and more vulnerable, and it was up to government to ensure that tests were available for them to do so.

“Schools return next week, and in the past this has seen Covid spreading among children, who then take it home to their families,” the Labour leader said. “As cases begin to rise in the more vulnerable age groups, so does concern for our elderly population. The government’s failure to prepare means it must now prioritise those who most urgently require tests, until it can get supply back to levels of demand.

Labour’s priorities, he said, would be protecting learning, the vulnerable and our emergency services and critical infrastructure. “Schools must stay open, because children have missed out on too much learning already.”

Geoff Barton, general secretary of the Association of School and College Leaders, welcomed the advice on mask wearing.

“Face coverings are already advised in communal areas for pupils in year 7 and above. Pupils are accustomed to their use and we are sure the reintroduction of face coverings in classrooms is something that schools and colleges will take in their stride.”

Earlier last year secondary school pupils in England were asked to wear masks in classrooms at a high point of infections though this was dropped when they slowed in the spring.

Before last night’s announcement, some secondary schools were already taking unilateral action, writing to parents saying masks would have to be worn in classrooms as part of efforts to avoid school closures.

In another sign of heightened concern, payouts worth hundreds of pounds are being offered to encourage ex-teachers to sign up to a government-inspired campaign to provide cover to schools hit by high levels of absences.

Supply agencies are promising cash or shopping vouchers for anyone who successfully “refers a friend”. Agencies are publicising the “call to arms” with online adverts offering minimum pay rates of about £130 a day.

An advert for Axcis Education says: “If you are not interested … but know someone else who might be … we offer up to £250 in shopping vouchers if you refer a friend to us and we place them in the job.”

With the full effects of Omicron still unclear, a leading expert on infectious diseases, Professor Mark Woolhouse of Edinburgh University, said a return to another full lockdown should be ruled out.

“There is still no good case for a full lockdown. Lockdowns aren’t a public health policy. They signify a failure of public health policy,” he said.

Britain got it wrong on Covid: long lockdown did more harm than good, says scientists.

“If we end up there again, it will be because we didn’t get the public health messaging right, because we failed to protect the vulnerable and because we didn’t order enough test kits – something which should have been attended to at the beginning of the month when it was obvious that Omicron would cause a huge surge in cases.”

In an interview with the Observer, Woolhouse added: “This was an epidemic crying out for a precision public health approach and it got the opposite. We did serious harm to our children and young adults, who were robbed of their education, jobs and normal existence as well as suffering damage to their future prospects, while they were left to inherit a record-breaking mountain of public debt.”

He added: “More generally, I hope we will quickly learn not to be surprised by new variants and not to respond to each one in an ad hoc fashion.”

Dan Poulter MP, a former health minister who also works as an NHS psychiatrist, said it was “unacceptable” that we were now facing testing shortages, which suggested lessons had not been learned. Poulter, a Tory MP, said ministers should ensure there was a permanent reservoir of PPE and testing equipment “as part of a national pandemic response reserve”

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