A third wave of Covid-19 cases could threaten schools after Easter if the Government abandons strict safety measures, a union has warned.

The NASUWT teaching union is calling on ministers not to water down guidance on face coverings in secondary schools and colleges ahead of the return of pupils for the summer term.

Secondary school and college pupils in England are currently being advised to wear face coverings wherever social distancing cannot be maintained, including in the classroom.

But the Government has said the measure will be reviewed at Easter.

Relaxing the rules in schools would send a message to pupils and parents that the threat of Covid has passed at a time when extreme caution is still needed

The NASUWT is concerned that ministers may relax the guidance as lockdown measures begin to be eased across the country.

Such a move would undermine Covid-19 safety and reduce pupils’ adherence to the wider safety controls in schools and colleges at a time when the risk of transmission remains high, the union claims.

A survey of more than 4,000 NASUWT members found that 75% support secondary school pupils being required to wear face masks in the classroom.

The findings have been published on the final day of the NASUWT’s virtual annual conference.

It came after the leaders of five education unions, including the NASUWT, called on the Government not to “rush into” removing face masks from class without careful consideration of the scientific evidence.

The joint letter from unions, to Education Secretary Gavin Williamson, argues that the current evidence “does not justify a change in policy on face coverings at the start of next term”.

But last month, MPs heard that school leaders had received “threatening letters” from parents who did not want their children to wear face coverings.

A straw poll, of over 300 NASUWT members, suggests that 67% of teachers support the continuation of the guidance on face coverings into the new term.

Dr Patrick Roach, general secretary of the NASUWT, said: “There is a real risk that the success of the vaccination programme to date, the easing of the lockdown and the reduction in current case numbers could lead to ministers being tempted to relax the Covid control measures in schools after Easter.

“In our view this would be a mistake.

“Ministers must model the behaviour they want to see in maintaining discipline and adherence to Covid safety measures.

“Relaxing the rules in schools would send a message to pupils and parents that the threat of Covid has passed at a time when extreme caution is still needed.

“We are not out of the woods yet and maintaining the highest levels of Covid security in our schools is critical as we move into the new term in order to protect the safety and health of teachers and learners.”

Speaking at the NASUWT’s virtual conference over the Easter weekend, Dr Roach called for a “cautious approach” to be maintained.

He told reporters: “There is evidence of Covid transmission within schools and thankfully fewer schools have been impacted than we saw for example at the back end of the autumn term, but nevertheless there are schools, there are bubbles and indeed there have been some examples of entire schools that have had to close since really opening on March 8.”

The union is also calling for financial compensation for teachers and education staff who have been left unable to work as a result of Covid-19.

It says more supportive sickness policies are needed that recognise the complex and changing nature of long Covid symptoms – which can see teachers going through extended cycles of illness and absence.

A Government spokeswoman said: “We have committed to reviewing our face covering guidance for schools over Easter.

“A decision will be made shortly, in partnership with health experts, about whether the evidence suggests these measures can continue into the summer term”.