Education Secretary Nadhim Zahawi has called on school leaders to encourage ex-teachers “to sign up” to help with Covid-19 staff shortages.

The minister said the Government was looking at what measures to put in place “to boost supply capacity”, adding that Department for Education (DfE) senior officials have begun discussing plans with key stakeholders.

It comes amid reports that some schools are experiencing “very severe low attendance” among teachers and pupils ahead of the Christmas break.

Headteachers’ unions have warned of possible disruption to in-person lessons in the new year if the Omicron variant leads to even higher staff absences.

School leaders 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.

In an email to school and college leaders ahead of the Christmas break, Mr Zahawi said: “We know that in areas with high absence a particular issue can be the availability of supply staff. We want to make sure that as many supply staff as possible are available to schools and colleges.”

The Education Secretary added: “We will work with sector leaders and supply agencies over the coming days to offer advice to ex-teachers who want to provide support to schools and colleges.

“We will help them to register with supply agencies as the best way to boost the temporary workforce available to the sector.”

In the plea to heads on Thursday, Mr Zahawi said: “From now, you can support this effort by using your own professional and personal networks to encourage others to sign up to offer temporary help.”

The DfE has also announced it will be extending its workforce fund for schools and colleges facing the greatest staffing and funding challenges amid Covid-19 to the February half-term.

It comes after the latest DfE figures showed that 2.4% of teachers and school leaders were absent from schools in England due to Covid-19 related reasons on December 9, up from 2.0% on November 25.

But education unions and Labour have warned that the Government’s actions are “unlikely” to be enough to solve the problem with staff shortages.

Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said: “This is all coming very late in the day for a situation which is already critical and has been so for some time, and the initiative will need to be well publicised, promoted and supported in order to have any degree of success.

“It is also important to emphasise that even then it is very unlikely to be enough to solve a problem at such a scale as this, and the Government does need to do much more in terms of supporting control measures, such as testing and ventilation, in order to reduce the risk of transmission of the virus.”

Shadow schools minister Stephen Morgan said: “This is a sticking plaster, and only part of what’s needed to keep children and staff safely in class next term.

“The Government’s failure to get a proper workforce plan in place leaves staff, children and parents relying on good will from retired staff and volunteers, many of whom face additional risks themselves.”

Kevin Courtney, joint general secretary of the National Education Union (NEU), said: “With this call for retired teachers to come forward the Government is admitting they are assuming there will be substantial disruption of education in January.

“It is important to say that this disruption is likely to be made worse because of the Government’s failure to put in place the mitigations and safety measures we have been calling for – on ventilation, air filtration, mask wearing and isolation of very close contacts.

“We still need those mitigations to be put in place – even to help with the effort of recruitment of temporary retired staff.”

Addressing possible disruption to education in January, Mr Barton added: “The difficulty will be if there are very high levels of staff absence as a result of the impact of the Omicron variant of Covid-19.

“It is likely that this would result in schools having to send home classes or year groups, or closing for on-site teaching, for short periods of time and providing remote education for those at home.”

Paul Whiteman, general secretary of school leaders’ union NAHT, said: “The reality is that if school staff become ill with Covid there are going to be challenges in maintaining provision, be that in-person or remote.

“Every single school leader will be determined to minimise any disruption to learning, but it does seem as though choppy waters lie ahead and that some form of disruption at the start of next term is looking sadly inevitable.”

Rebecca Boomer-Clark, chief executive of Academies Enterprise Trust (AET), which runs 57 schools, said: “We’re making sure all children from Year 3 through to Year 13 are going home for the Christmas holidays with a chromebook and MiFi dongle where needed, so that if we have to move to virtual learning everyone is set up and ready to go.”

Vulnerable children in Kingston upon Thames are also being provided with laptops before Christmas as part of contingency plans for January.

Rebecca Bakewell, head of school at City Academy in Birmingham, said she wants to make sure students have everything they need to continue learning in case there are closures in the new year.

She added: “That includes making sure every child has access to an electronic device and knows how to engage with online lessons, as well as access to as many resources as possible at home. Preparing now will also give students reassurance over the Christmas break.”

In Wales, schools will have two days at the start of term in January to assess staffing capacity and to make plans for moving to remote lessons if needed.

In England, secondary schools will receive a “small amount of flexibility” on when they return so they can test pupils for Covid-19 after the Christmas break, education minister Alex Burghart said.

But he told MPs on Wednesday: “The Government is committed to ensuring schools open in January as normal.”

Health minister Gillian Keegan has suggested that children aged 12-15 getting their coronavirus vaccines should be enough to keep schools open in January.