Schools that force pupils to wear face masks could face legal action if they are deemed to be doing so "irrationally", it is claimed.
An expert in public law has told how schools do not have a mandate for plans to make face coverings compulsory in school settings.
George McLellan of the law firm DLA Piper told the Telegraph how schools could be deemed to be using "disproportional" power and not following Government guidance.
School leaders are planning to make face covering compulsory when schools reopen in September, in a bid to prevent the spread of coronavirus.
But Mr McLellan said guidance from the Government does not mandate them in classrooms.
And he warned that parents could bring a judicial review against schools if they are deemed to be acting with "unreasonableness or irrationality".
He said: "The primary ground for judicial review would be unreasonableness or irrationality.
"The concern with masks is that there is no rational basis for them to be required. We would say there is a lack of proportionality of requiring children in schools to wear masks."
He described plans to push ahead with the rule as "manifestly absurd".
DLA Piper has been backed by parents’ campaign group UsForThem.
Co-founder Molly Kingsley said there was anger among parents about the plans, and her organisation would back parents in bringing a judicial review against a school.
She said: "Based on the anger we have seen among our group, there is a very visceral reaction among parents to face masks in schools.
"This is something parents would want to challenge and we would want to support them."
On July 15, we reported how Health Secretary Matt Hancock had no plans for teachers and office workers to wear masks when they return to work.
He told ITV's Lorraine show: "The reason is, that where a mask can be useful is where you're seeing somebody for a short to medium amount of time.
"If you're in the same room as them, all day, like whether in an office together, or for instance, teachers in schools, then we don't think masks make much difference, because you're in that same space with the same people."
He added: "Whereas on public transport, in shops, you're seeing different people and for relatively short periods of time, so the mask can help."
At least 10 UK schools have already taken matters into their own hands and are making face masks mandatory or “very strongly encouraged” when pupils return to school.
But the Government has ruled out making them mandatory in secondaries.
Teaching unions have called on ministers to look again at the rules so that pupils and staff have to wear masks after the summer holidays.
Patrick Roach, general secretary of the NASUWT teachers’ union, said: “The Government’s guidance for schools is now out of step with wider public health guidance and guidance to other employers where it is recognised that where physical distancing cannot be assured, face masks should be worn.
“So there is a strong argument that face masks should also be made compulsory for children when they return to secondary schools in September.”
Julie McCulloch, director of policy at the Association of School and College Leaders, said she expected “most schools” to follow the guidance but there is “a fair degree of confusion about why face coverings are required in some settings but not in schools”.
The GMB union has written to Education Secretary Gavin Williamson urging him to adjust the “double standards” in the Government’s guidance on face masks.
National officer Karen Leonard said it was “plain common sense” that teachers and other workers in schools should be able to wear coverings.
“Changing the rules for buses and shops to enforce the wearing of masks while actively discouraging those working in schools from wearing them is causing untold confusion,” she said.
“It’s time for Gavin Williamson and his colleagues to rethink their position, provide clarity and consistency for our valuable school staff, and ensure PPE - including face masks - is available and can be worn by staff in schools where required.”
The Government has so far resisted calls to change its guidance on face coverings for school settings.
A Department for Education spokesperson said: “We have set out the 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 from September.
“This does not include the wearing of face coverings as we believe the system of controls laid out adequately reduced the risk of transmission to both staff and students.”
Public Health England does not recommend their use as pupils and staff are “mixing in consistent groups” and using them incorrectly could increase the risk of infection.
Some European countries, including Germany, have decided to make masks compulsory for teachers and pupils.
In Spain, children aged between 11 and 18 must wear them if they can’t keep at least 1.5m apart while in France, teachers do if they’re 1m or less away from a child.
