The former head of Ofsted will return to teaching next month to help a school with high staff absences.

Sir Michael Wilshaw, the former chief inspector of schools in England, will teach history to pupils in a south London school in January to help a headteacher who is expecting more absences in the new year.

It comes after Education Secretary Nadhim Zahawi has urged ex-teachers to sign up to help with Covid-19 staff shortages in the new year.

But school leaders have warned that the initiative is unlikely to happen quickly enough to help schools when they return in January – especially as retired teachers could be put off by rising Covid-19 cases.

The highly transmissible Omicron variant is expected to cause even higher staff absence levels in the spring term, and headteachers’ unions have warned of possible disruption to in-person lessons.

Former head Sir Michael, who is over 70, said schools should be kept open “at all costs” as he warned that Covid-19 has increased inequality in education.

Speaking to BBC Radio 4’s Today programme, he said: “We’ve got to keep schools open whatever and if that means people like me going back into the classroom so be it.”

Sir Michael, who temporarily returned to teach in a north London school during the first Covid-19 wave, told Sky News that members of his family had previously advised him not to go back into the classroom.

But he said he was glad he did. “I really enjoy getting back into school and engaging with children and it’s something that I feel is a moral imperative,” Sir Michael said.

The Government is pleading with recently retired teachers, or those who trained as teachers and changed career, to “find even a day a week for the spring term to help protect face-to-face education”.

It comes amid reports that some schools have experienced very low attendance among teachers and pupils ahead of the Christmas break.

Heads and academy chain chiefs are preparing for the possibility of having to switch to online learning next term – and some pupils have been asked to take laptops home before Christmas just in case.

Former secondary school head Stuart McLaughlin, who retired in April 2020 as he felt “worn down” by the “high-stakes” accountability system, said there is nothing that would make him want to return.

He told the PA news agency: “Especially as I think it’s even more challenging for heads now than when I left. Trying to deal with Covid, trying to deal with the staffing problems.”

Mr McLaughlin, who stepped down from headship at Bower Park Academy in Romford in east London at the age of 59, said: “People retire for a reason. They kind of feel worn down, or they think it’s just time to stop teaching, and I can’t see why if people have made that decision they would then rush back now.”

He told PA: “I’d be really surprised if large numbers decide to go back. It might be slightly different if you have only just retired, but I think if anyone’s been retired for a while, I can’t see them wanting to go back.

“Most people who are retired are older and you’re then going back into a risky environment. So there is an element of putting yourself at risk if you go back into the classroom environment.”

Mr Zahawi has said former teachers who are available to return should apply on the Get Into Teaching website and ideally start the process before Christmas Eve so they can join the workforce from January.

James Bowen, director of policy for school leaders’ union NAHT, said members are “already questioning whether this is likely to be an effective solution”.

He said: “At this stage there has to be major question marks over how many retired teachers will be looking to go back into the classroom when transmission rates are so high and increasing.

“Similarly, it’s not clear how people currently in other jobs would suddenly be able to drop what they’re doing and return to teaching.”

Julie McCulloch, director of policy at the Association of School and College Leaders (ASCL), said: “It remains to be seen whether this initiative can attract ex-teachers in the kind of numbers to make any real difference, but we feel it is highly unlikely it will happen quickly enough to help schools when they return in the first week of January.

“We also question whether ex-teachers will have much appetite for returning to classrooms given the high number of students who have tested positive in recent weeks.

“They may have been more encouraged had the Government’s responses to providing schools with high-quality ventilation equipment and to urging students to test at home not been so lacklustre.”