The Education Secretary has written to parents urging them to continue with lateral flow testing.

His plea to families comes in the wake of calls for the testing programme to be suspended altogether after analysis by The Telegraph revealed that up to 60 per cent of "positive" tests a week are coming back negative when checked.

In a letter to parents on Friday, Gavin Williamson insisted that asymptomatic testing has played a “vital role” in the UK’s response to the pandemic and is helping to break chains of transmission.

“With the increase in cases with variants of concern, it is important to continue regular testing in order to detect cases of coronavirus, stay ahead of the virus and keep Covid out of the classroom,” he said.

“This means that regular asymptomatic testing for all will continue, and we need you and your children who are in secondary school or college to carry on testing at home, twice a week.”

When schools reopened on March 8, secondary school pupils and their families were asked to take two rapid antigen tests each week and report any positive results to their school.

So far more than 50 million lateral flow tests have been carried out on youngsters, leading to thousands of pupils and their social bubbles being forced to self-isolate for 10 days.

But an analysis of NHS Test and Trace data by The Telegraph showed that, in secondary schools, one-third of lateral flow tests checked against the gold-standard Polymerase Chain Reaction (PCR) test have come back negative. In one week in March, that rose to 60 per cent.

Earlier this week Professor Sir Andrew Pollard, who led the Oxford vaccine programme, warned that mass testing was leading to such huge disruption in schools that it may be worth vaccinating youngsters to stop the chaos.

"If children are not severely affected, if they’re not major drivers of transmission, the testing itself is picking up lots of cases – causing classes to be sent home and so on – we’ve got to get to a point where we’re not impacting on education," he said. "And I think that impact on education could be a reason for vaccination.

"If children aren’t very much affected, then the testing is obviously not protecting them as they’re not very affected. So is the testing being done to protect other people?"

Covid school regulations

On Thursday, 23 British academics from universities including Oxford, Cambridge and University College London wrote to Mr Williamson to warn that lateral flow testing posed a danger for schools.

They are concerned that ongoing contact tracing trials could spark a wave of new infections and have called for them to be suspended.

Dr Deepti Gurdasani, a senior lecturer at Queen Mary University of London and one of the letter’s authors, pointed out that according to the UK medicine regulator, the MHRA, mass testing should have at least 80 per cent accuracy to “rule in” infection but this condition is not being met in schools. 

What’s the difference between a PCR test and a lateral flow test?

“The concerns are that if messaging isn’t clear that these tests cannot rule out infection, a negative test may change behaviour and may be used for ‘rule in’ purposes even if it shouldn’t,” she said.

“Also, people with symptoms may undertake this because it’s faster and easily accessible, which is of course problematic, because of the low accuracy of these tests.”

Dr Gurdasani, a clinical epidemiologist and statistical geneticist by training, added that it makes “no sense” to have invested billions in the tests while not supporting people with isolation.