Hundreds of thousands of pupils are returning to the classroom this week to a relaxation of Covid-19 safety measures.

Headteachers’ unions have warned that fewer mitigations this term could lead to rising infections among school-aged children, with one leader suggesting it is a “case of hit and hope” from the Government.

Schools and colleges in England no longer have to keep pupils in year group “bubbles” to reduce mixing, and face coverings are no longer advised.

Children do not have to isolate if they come into contact with a positive case of Covid-19. Instead, they will need to get a PCR test and isolate only if positive.

But all secondary school pupils are being invited to take two lateral flow device tests at school – three to five days apart – in England on their return to class.

We are also concerned that there will be disruption in the autumn term with rising cases amongst school age children

Secondary schools and colleges are allowed to stagger the return of pupils across the first week to manage the Covid-19 asymptomatic testing process.

Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said it seems “bizarre” that the safety measures have been eased for this term despite warnings from scientists about higher cases.

He told the PA news agency: “There was a raft of mitigations in place at the end of the summer term and it does seem bizarre that we have gone from that to far less stringent measures this term, with little notion of how effective this will be and with scientists warning about the likelihood of an exponential increase in infections among school-age children.

“It does feel a little like a case of hit and hope on the part of the Government.”

Pupils in England and Wales are starting to return to the classroom this week.

Most schools in Northern Ireland returned last week, but all remaining schools will open on Wednesday.

Schools in Scotland have already returned after the summer break and the reopening is believed to have contributed to a rise in cases north of the border.

Mr Barton added: “As the majority of students prepare to return to the classroom this week there is a critical need for stability and for the Government to keep the situation under review and be ready to respond with more support for schools and colleges if it is needed.

“We simply cannot have a situation in which we again see an alarming spiral in the number of children out of school, and must be on guard against the health risks of infections.”

He also called on the Joint Committee on Vaccination and Immunisation (JCVI) to make a decision about whether vaccines for younger pupils should happen.

The NHS is preparing to ensure it is ready to potentially offer Covid-19 vaccines to all 12 to 15-year-olds in England from early September, although a decision has yet to be taken about this age group.

Schools and colleges in England are still being encouraged to maintain increased hygiene and ventilation this term, and secondary school and college pupils have been asked to continue to test twice weekly at home.

Last month, the Government announced a £25 million investment for rolling out around 300,000 carbon dioxide monitors across state schools and colleges in England to help reduce the spread of Covid-19.

The safety measures being advised differ slightly across the four nations.

It does feel a little like a case of hit and hope on the part of the government

Paul Whiteman, general secretary of school leaders’ union NAHT, is worried the removal of many mitigations could lead to further “disruption”.

He told PA: “The concern is that the Government has removed nearly all of the mitigations we had when schools broke up. It could put school leaders in an awkward position with parents who may not understand all the changes the Government has mandated.

“We are also concerned that there will be disruption in the autumn term with rising cases amongst school age children. This may need emergency procedures on the advice of local authority health leads or central government. This will cause further confusion.”

He added that the introduction of C02 monitors will only confirm where poor ventilation exists.

Mr Whiteman said: “In some classrooms it is not as simple as opening a window, especially with the onset of winter.

“We’re going back to school in September with the same picture on ventilation as we had 12 months ago. That isn’t a good situation to be in. The Government needs to equip schools properly to avoid further disruption and fast.”

Earlier this week, Education Secretary Gavin Williamson said parents should make sure their children were tested regularly for coronavirus as he warned youngsters not to get “carried away” when schools return.

His comments came after experts warned that it is “highly likely” there will be large levels of coronavirus infection in schools by the end of September.

A Department for Education spokeswoman said: “Education remains a national priority, and the success of the vaccine programme means schools and colleges will deliver high-quality, face-to-face education to their pupils, with minimal disruption.

“The measures in place strike the right balance between making schools safe – with enhanced ventilation, Covid testing and vaccinations of older students and staff – and reducing disruption by removing bubbles and face coverings.”