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Boris Johnson has made a personal plea to parents to send their children back to school in September.

The prime minister said the risk of catching coronavirus in schools is “very small”, and that pupils face greater harm by continuing to stay at home.

On Sunday the chief medical officers and deputy chief medical officers of England, Scotland, Northern Ireland and Wales issued a joint statement reassuring parents it was safe to send their children back to school.

They said “very few, if any” children and teenager would come to long-term harm from catching Covid-19 by attending school.

But shadow education secretary Kate Green criticised the government for being “asleep at the wheel” and having failed to provide the necessary details to schools to reopen.

“The government has to make the conditions suitable and safe for staff, for students,” Green told ITV’s Good Morning Britain on Monday. “It’s been asleep at the wheel. It’s been not paying the attention that schools need, to the details of how they’re going to re-open.

“There hasn’t been information for school leaders, so that they can’t plan what they might have to do if there was a sudden spike in the local infection rate and the guidance that has come out I think has been – it’s been contradictory, it’s been confusing, it came very late, shortly before the summer holidays.

“So I think better support for schools would have made the lives of staff much, much easier and of course over the last couple of weeks… we wouldn’t have been in quite the position we’re in if the Government hadn’t had to waste time sorting out its exams fiasco.”

Teaching unions have also called for greater clarity on what to do if there is a spike in cases as well as to provide extra funding for school cleaning after it was discovered that heads were struggling to make premises Covid-secure.

In a statement released on Sunday evening, Johnson said: “I have previously spoken about the moral duty to reopen schools to all pupils safely, and I would like to thank the school staff who have spent the summer months making classrooms Covid-secure in preparation for a full return in September.

“We have always been guided by our scientific and medical experts, and we now know far more about coronavirus than we did earlier this year.

“As the chief medical officer has said, the risk of contracting Covid-19 in school is very small and it is far more damaging for a child’s development and their health and wellbeing to be away from school any longer.

“This is why it’s vitally important that we get our children back into the classroom to learn and to be with their friends. Nothing will have a greater effect on the life chances of our children than returning to school.”

Johnson said earlier this month that getting all children back to school full-time in England in September is the “right thing for everybody”, insisting they are “safe” and “Covid secure”.

However, teachers, scientists, opposition politicians and the children’s commissioner for England Anne Longfield have previously called for improvements to testing before pupils return.

Labour leader Keir Starmer said government incompetence and the “week of chaos” over exam results was putting the plans to get all children back to school at “serious risk”.

Kevin Courtney, joint general secretary of the National Education Union (NEU), said: “Government advice needs to cover the possible self-isolation of bubbles and, in extremis, moving to rotas or to more limited opening.

“It needs to cover advice to heads about the protections needed for staff in high-risk categories if infection rates rise.”

Schools in Northern Ireland opened on Monday, while those in Scotland reopened earlier this month. English and Welsh schools are due to reopen their doors in September.

Analysis published on Sunday by Public Health England (PHE) showed there were 67 single confirmed cases, four “co-primary cases” (two or more linked cases diagnosed at the same time) and 30 coronavirus outbreaks in schools during June. 

It said the majority of cases were among staff and added further school closures may be necessary but should “be considered only in extremis”.