Teachers have been accused of being “overcautious” with self-isolation as it has emerged the number of children being sent home to isolate has quadrupled despite Covid cases barely rising.

Last week, 172,000 pupils were self-isolating after potentially coming into contact with a positive Covid case at school, up from 40,000 the previous week.

But the number of positive cases rose from 7,000 to just 9,000 over the same period of time, leading to claims that schools are sending more pupils home than necessary.

Liz Cole, co-founder of the parent campaign group UsForThem, said that a “huge number” of parents had reported that entire year groups were being banned from the classroom for 10 days after just one fellow student in their cohort had tested positive. 

“There are many examples of a single positive case resulting in 150 to 190 children being sent home,” she said.

“What we are hearing is that the messaging around the delta variant is leading teachers to take an overcautious approach.

“Parents are becoming increasingly frustrated and angry given the inconsistency between these rules that are being applied to children in schools versus the rules for professional football bubbles.”

Map of UK’s seven-day Covid-19 infection rate, by local authority

On Monday, England players Mason Mount and Ben Chilwell were told to self-isolate after chatting to Scotland midfielder Billy Gilmour in the Wembley tunnel. 

Gilmour subsequently tested positive for Covid-19, but none of his Scottish team mates have been forced to isolate on the advice of Public Health England.

Ms Cole said the overcautious approach being applied in schools could also be down to decisions by local public health teams, who advise headteachers on how many students to send home if there are two or more cases of Covid within two weeks. 

All school children should be organised into bubbles, according to official guidance. These bubbles should be an “appropriate size” to ensure that there is as little contact and mixing as possible between pupils.

The Department for Education (DfE) said that bubbles should be “no larger than circa 30 children” adding that where possible smaller bubbles should be maintained.

But parents are increasingly reporting that a “nervousness” among schools about the delta variant is leading to entire year groups being sent home. “There is more anxiety and heightened levels of caution around this variant,” Ms Cole said.

Last week, Gavin Williamson, the Education Secretary, wrote to parents urging them to continue with lateral flow testing. Every secondary school pupil and the members of their household are meant to take two of the rapid antigen tests each week at home and report any positive results to their school.

Mr Williamson’s plea came in the wake of calls for the testing programme to be suspended after analysis by The Telegraph revealed that up to 60 per cent of "positive" tests a week were coming back negative when checked.

It came after British academics from universities including Oxford, Cambridge and University College London wrote to him to warn that lateral flow testing posed a danger for schools and called for it to be suspended.

According to the DfE figures, Covid-related pupil absence in English schools is now at its highest since all schools fully reopened in March. Headteachers said the data was “extremely worrying” and have told ministers to “think urgently” about how disruption to education could be reduced in the next academic year.

A government spokesperson said: “Schools across the country continue to have robust protective measures in place, including regular twice-weekly testing to break chains of transmission and keeping pupils in smaller group bubbles.

“We are also taking additional measures in areas where there is a high prevalence of the virus, including increasing the availability of testing for staff, pupils and families and working with directors of public health on further measures to reduce local transmission.

“Absence in schools continues to reflect wider community transmission. Where students have to self-isolate, schools are providing high-quality remote education.”