Secondary school children in England are to get rapid turnaround coronavirus tests starting in January, the government announced this week.

But in recent days, the health secretary Matt Hancock and the schools minister Nick Gibb have been challenged on how reliable the “lateral flow tests” – which give results in around 30 minutes – really are.

On this morning’s BBC Breakfast, interviewer Naga Munchetty put it to Mr Gibb that the tests “detected just 48.9 per cent of Covid-19 infections in asymptomatic people”. The schools minister replied: “No, about a third have false negatives”. He added that pupils would get two tests each, three days apart.

There was a similar exchange in the House of Commons earlier in the week, when SNP MP Philippa Whitford confronted Mr Hancock with the results of a study that “revealed a sensitivity of just 48 per cent, meaning that over half of those with the virus would be falsely reassured they were negative”.

In his reply, the Health Secretary said “the lateral flow tests find around 70 per cent of those who are infectious” and that he would “urge” Dr Whitford – herself a former hospital consultant – “to go back, to study the details”.

But despite both ministers’ denials, the 48 per cent figure is supported by a SAGE paper dated 25 November. It compared the performance of the lateral flow tests used in the Liverpool mass-testing pilot with the “PCR” laboratory tests that have thus far formed the bulk of the UK’s testing programme.

So how did Mr Hancock arrive at the “70 per cent” figure (the mirror image of Mr Gibb’s “a third have false negatives” claim)?

They’re citing research by the government’s Porton Down lab and the University of Oxford dated 8 November. The teams found an “overall sensitivity of 76.8 per cent”, with over 95 per cent of people with high “viral loads” picked up by the test.

So how do we have such a wide range of results? The answer seems to be context. The Liverpool research was looking at real-world tests carried out “in the field” – while the Porton Down/Oxford figures come from several different settings.

The Porton Down/Oxford team found that the tests were most accurate when carried out by lab scientists (picking up 79 per cent of positive cases), slightly less so when done by trained healthcare workers (73 per cent) and significantly worse when carried out by “self-trained members of the public” (58 per cent).

So what does that mean for the rollout of lateral flow tests for schools?

The government is due to publish “operational details” next week on how the 11 billion promised tests will be administered across England. But according to an NHS “handbook” obtained by Schools Week, headteachers will be expected to get school staff, volunteers, school and/or retired nurses and agency workers to carry out and/or supervise tests. That suggests some, if not all, will be relative beginners when it comes to testing protocols.

If that’s the case, it’s likely that the lateral flow tests will pick up rather less than 70 per cent of positive cases in schools, despite ministers’ claims this week. Though of course, the chances of finding a positive case will increase with a second test, which the government says pupils will receive three days after their first.

The Department of Health and Social Care told FactCheck: “With up to a third of individuals with Covid-19 not displaying symptoms, broadening testing to identify those showing no symptoms and who can infect people unknowingly will mean finding positive cases more quickly and break chains of transmission.

“The country’s leading scientists have rigorously evaluated the Lateral Flow Test and confirmed the accuracy of the tests for asymptomatic testing.”