Boris Johnson has abandoned advice that pupils should not wear face masks in English secondary schools.
The prime minister performed his latest U-turn in the face of growing pressure from headteachers, teaching unions and medical experts.
Face coverings will be mandatory for children in all schools that lie in areas subject to stricter coronavirus restrictions.
But while headteachers will retain discretion over the use of face masks in schools in other parts of England, the government will drop guidance that they should not be used.
A statement issued by the Department for Education insisted the climbdown had come as a result of a change in the World Health Organisation's (WHO) advice - despite that shift happening four days ago.
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The WHO issued new guidance on 21 August, saying "children aged 12 and over should wear a mask under the same conditions as adults, in particular when they cannot guarantee at least a one-metre distance from others and there is widespread transmission in the area".
Wales' health minister Vaughan Gething had asked a scientific advisory group to consider the current COVID-19 guidance for the nation's schools, which are due to return next week.
That came hours after the Scottish government revealed secondary school pupils in Scotland would have to wear face coverings when moving through corridors and other communal areas from next Monday.
Sturgeon: Face coverings to be worn in Scottish schools
Every pupil over the age of five will also have to wear face masks on school buses in Scotland.
Meanwhile, Northern Ireland updated its guidance on face coverings to recommend they be worn by teachers and pupils in corridors and other communal areas of all secondary schools.
Referring to the shift in policy for English schools, Education Secretary Gavin Williamson said: "Our priority is to get children back to school safely.
"At each stage we have listened to the latest medical and scientific advice. We have therefore decided to follow the World Health Organisation's new advice.
"In local lockdown areas children in year seven and above should wear face coverings in communal spaces.
'Schools are safe' - PM
"Outside of local lockdown areas face coverings won't be required in schools, though schools will have the flexibility to introduce measures if they believe it is right in their specific circumstances.
"I hope these steps will provide parents, pupils and teachers with further reassurance."
However, the prime minister faces resistance to the move from within his own ranks, with Tory MP Marcus Fysh voicing his oppostion after it emerged the U-turn may be imminent.
"Masks should be banned in schools," he said on Twitter.
"The country should be getting back to normal not pandering to this scientifically illiterate guff."
Officials announced another 1,184 confirmed COVID-19 cases across the UK on Tuesday - up from 853 on Monday - and 16 more deaths among people who had tested positive for the virus.
BORIS Johnson has rubbished "nonsense" claims he will quit in 6 months because of his ill-health from his battle with coronavirus.
The PM said he was feeling "far better" than ever after losing 1.5 stone after a report claimed chief adviser Dominic Cummings' father-in-law had told a journalist he would resign.
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No10 said it was "utter nonsense" Boris Johnson would be resigningCredit: PA:Press Association
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The PM visited Appledore Shipyard in Devon which will reopen after it was bought by InfraStrataCredit: PA:Press Association
During a visit to Appledore Shipyard in North Devon the PM addressed the rumours, telling Devon Live: "It's absolute nonsense! I am feeling, if anything, far better as I've lost some weight. Not enough, but I have lost at least a stone and a half.
"I feel much much better for having lost, by my standards, quite a lot of weight."
The report by The Times diary column claimed chief adviser Dominic Cummings' father-in-law suggested that the PM was ready to step down because of the toll coronavirus has taken on him.
The rumours cited journalist Anna Silverman, who had visited Chillingham Castle in Northumberland, which is home to Sir Humphry Wakefield, the father of Mr Cummings' wife Mary.
Sir Humphry apparently "merrily" told Ms Silverman that Mr Johnson is "still struggling badly with having had Covid-19" and "will stand down in six months".
"If you put a horse back to work when it's injured it will never recover," it reported him as saying.
But the extraordinary claims have been laughed off by Downing Street.
A No10 spokesperson told The Sun: "This is nonsense".
The head of England's exams regulator, Sally Collier, has quit after thousands of students' marks were downgraded for exams they were unable to sit.
Ofqual chief Ms Collier has been under fire for a controversial algorithm which changed GCSE and A-level marks, making them unfair, according to heads.
It also led to many A-level students losing university places they had been offered, and a crunch on degree places.
Education Secretary Gavin Williamson thanked her for her commitment.
He added: "Moving forward, my department will continue to work closely with Ofqual's leadership to deliver fair results and exams for young people."
Scotland's results
Exams for GCSE and A-level students were cancelled by Mr Williamson in March, just before schools were closed, when the nation was in the grip of the coronavirus pandemic.
A system to ensure pupils could still get their grades was drawn up by Ofqual which involved teachers and schools predicting grades for their pupils from a whole range of evidence
These were then sent to the exams regulator to be moderated so as to avoid more students than usual getting higher grades.
The now discredited algorithm used information on schools' past performance to moderate the grades, drawing complaints that pupils were being judged on the efforts of the predecessors.
Scotland, which used a similar system, rowed back on the arrangement after it became apparent that many bright but disadvantaged pupils were downgraded.
Scotland's education secretary John Swinney announced a switch to teacher-assessed grades and results were re-issued.
Late U-turn
But it was not until two weeks later that his counterpart in England, Gavin Williamson, decided to revert to what are known as centre-assessed grades.
This meant that hundreds of thousands of A-level results had to be re-issued and GCSE results were rushed through to schools to be released three days after the government U-turn.
And hundreds of thousands of the BTec students have still not received their grades after the exam board, Pearson, made a last minute decision to re-grade.
The previous regulator, Dame Glenys Stacey, has been asked to step in.
She will run the next stage of the exams process on a temporary basis until December, the Ofqual board said, along with the chief of Ofsted, Amanda Spielman, who previously worked at Ofqual.
'Full focus'
Mr Williamson said: "Following Sally Collier's decision to step down as Ofqual's Chief Regulator, I'd like to thank her for the commitment she has shown to the role over the last four years and wish her well for the future.
"I welcome Ofqual's announcement that Dame Glenys Stacey is to assume a temporary leadership role as acting Chief Regulator and also the new internal governance arrangements put in place with Ofsted support.
"This will make sure Ofqual can fully focus on the important functions it must deliver as the independent regulator for qualifications, examinations and assessments in England."
Association of School and College Leaders General Secretary Geoff Barton said: "This move follows the failure of the statistical model that led to this year's grading fiasco, but the fault is not hers alone.
"Ministers have questions to answer over the extent to which they scrutinised and challenged the methodology and reliability of the statistical model, particularly given the enormity of the task and the importance of getting it right."
National Education Union Joint General Secretary Kevin Courtney said: "Someone had to take responsibility for the exams fiasco, but the issue runs far deeper than the actions of one chief executive.
"We have no sure way of knowing where the balance of fault lies, but we can be quite certain that Gavin Williamson gave direction to Ofqual that there should not be grade inflation and all candidates should get a fair grade."
The head of England's exams regulator, Sally Collier, has quit after thousands of students' marks were downgraded for exams they were unable to sit.
Ofqual chief Ms Collier has been under fire for a controversial algorithm which changed GCSE and A-level marks, making them unfair, according to heads.
It also led to many A-level students losing university places they had been offered, and a crunch on degree places.
Education Secretary Gavin Williamson thanked her for her commitment.
He added: "Moving forward, my department will continue to work closely with Ofqual's leadership to deliver fair results and exams for young people."
Scotland's results
Exams for GCSE and A-level students were cancelled by Mr Williamson in March, just before schools were closed, when the nation was in the grip of the coronavirus pandemic.
A system to ensure pupils could still get their grades was drawn up by Ofqual which involved teachers and schools predicting grades for their pupils from a whole range of evidence
These were then sent to the exams regulator to be moderated.
The now discredited algorithm used information on schools' past performance to moderate the grades, drawing complaints that pupils were being judged on the efforts of the predecessors.
Scotland, which used a similar system, rowed back on the arrangement after it became apparent that many bright but disadvantaged pupils were downgraded.
Scotland's education secretary John Swinney announced a switch to teacher-assessed grades and results were re-issued.
Late U-turn
But it was not until two weeks later that his counterpart in England, Gavin Williamson, decided to revert to what are known as centre-assessed grades.
This meant that hundreds of thousands of A-level results had to be re-issued and GCSE results were rushed through to schools to be released three days after the government U-turn.
And hundreds of thousands of the BTec students have still not received their grades after the exam board, Pearson, made a last minute decision to re-grade.
The previous regulator, Dame Glenys Stacey, has been asked to step in.
She will run the next stage of the exams process on a temporary basis until December, the Ofqual board said, along with the chief of Ofsted, Amanda Spielman, who previously worked at Ofqual.
'Full focus'
Mr Williamson said: "Following Sally Collier's decision to step down as Ofqual's Chief Regulator, I'd like to thank her for the commitment she has shown to the role over the last four years and wish her well for the future.
"I welcome Ofqual's announcement that Dame Glenys Stacey is to assume a temporary leadership role as acting Chief Regulator and also the new internal governance arrangements put in place with Ofsted support.
"This will make sure Ofqual can fully focus on the important functions it must deliver as the independent regulator for qualifications, examinations and assessments in England."
Association of School and College Leaders general secretary Geoff Barton said: "This move follows the failure of the statistical model that led to this year's grading fiasco, but the fault is not hers alone.
"Ministers have questions to answer over the extent to which they scrutinised and challenged the methodology and reliability of the statistical model, particularly given the enormity of the task and the importance of getting it right."
In England, despite official guidance against face coverings, some schools are already preparing to use them.
The Oasis academy trust, with more than 50 schools in England, is providing visors for its teachers - and secondary pupils will have to wear masks in corridors.
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On Tuesday, the ASCL head teachers' union said parents and schools needed more clarity and "reassurance" over the evidence for not allowing masks.
The head teachers' union said it would be "prudent" to reconsider the opposition to allowing masks, in the light of the policy in Scotland and the recent guidance by the World Health Organisation, which recommended face coverings for the over-12s.
The heads' union asked what schools should say if teachers or pupils said they wanted to wear a face covering - and for a "clear direction one way or another".
The union's leader Geoff Barton also urged "if there is going to be any U-turn by the government that it does this sooner rather than later, because the start of the new term is imminent".
On a visit to Devon, the prime minister emphasised the safety of the return to school in September, saying "all our scientific advice is that schools are safe, it's absolutely crucial people understand that".
On whether face masks should be allowed in school, Mr Johnson said: "We'll look at the changing medical evidence as we go on, if we need to change the advice then of course we will."
Despite the current guidance against using masks, it seems some schools are already making their own decisions.
Steve Chalke, chief executive of the Oasis academy trust, said there was a responsibility to make schools "as safe as we possibly can" - and that meant using masks and visors.
Like wearing a school uniform, he said wearing masks would become "part of what we do" and would be part of a wider safety plan, including hand washing and keeping pupils apart in separate "bubbles".
But in secondary school corridors and shared areas, where pupils could not be kept apart, Mr Chalke said masks would be required.
"We're using our common sense for our schools and our buildings," he said.
'Nervous parents'
It would help to protect teachers as well as pupils, he said, including those who might have underlying health conditions or who are in a more vulnerable age group.
Mr Chalke said schools leaders had to make a "moral choice" on how best to make schools safe on the scientific advice available.
He also thought using masks, which will be provided, might increase the confidence of parents "nervous" about sending their children back to school.
A secondary school in Kent, Sir Roger Manwood's School in Sandwich, is expecting pupils and staff to wear masks - with pupils each being given three washable masks.
The government's safety guidance, issued in July, says Public Health England does not recommend using face coverings in school.
As pupils would be in their own separate "bubbles" there is no need for masks, says the guidance, which warned that "misuse" of face coverings could "inadvertently increase the risk of transmission".
Labour's Shadow Education Secretary Kate Green called on the prime minister to "act quickly to give certainty to parents and teachers who are just days away from schools reopening".
"There is a growing body of evidence that the use of facemasks in communal areas in secondary schools helps protect students and staff and drive down transmission," she said.
A Department for Education spokeswoman said: "We have consistently followed Public Health England advice, which does not recommend the use of face coverings in schools because there are a range of protective measures in place, including children staying in consistent groups.
"We have set out the system of controls schools should use, including cleaning and hygiene measures, to substantially reduce the risk of transmission of the virus when they open to all children in the coming weeks."
