Controversial rapid lateral flow tests 'can detect most infectious cases' of coronavirus, a Government-led study has claimed amid concerns about their reliability.
Oxford University scientists who carried out the research found the devices, which give a result within half an hour, catch between 84 and 90 per cent of Covid-positive people.
Number 10 has spent more than £1billion on at least half a dozen different lateral flow tests and is offering them to councils across England to be used in schools, universities, care homes and in critical businesses to keep the country ticking over until everyone is vaccinated.
The Oxford study found the Government's most sensitive lateral flow devices (LFD) detect 90.5 per cent of Covid cases, while the least sensitive catch 83.7 per cent of infectious people.
Tim Peto, professor of medicine at Oxford and senior author of the paper, said the tests could be a 'game-changer' in the UK's Covid fight, although he admitted they 'are not perfect'.
However, the research only looked at the effectiveness of the tests when administered by trained health professionals. Previous studies have shown that when people do them themselves, as is the plan for Boris Johnson's Operation Moonshot, their accuracy plummets.
The tests missed 60 per cent of infected people in a mass trial in Liverpool when people swabbed themselves.
Rouxel Maryline, a lorry driver travelling to Caen, France, via Portsmouth tonight at 11pm, receives a lateral flow test
Scientists have for weeks been sounding the alarm about LFDs over fears about their accuracy and because previous studies have shown they can only detect Covid in people with high viral loads - the amount of virus in the nose and throat.
Researchers looked at nearly 20,000 PCR-positive samples across the UK that were submitted to NHS Test and Trace.
Department of Health puts NHS branding on rapid Covid tests so it can get around manufacturer's instructions that people should NOT swab themselves
The Department of Health is repackaging controversial rapid coronavirus tests as NHS self-tests in what critics claim is a 'bizarre' move to get around manufacturer instructions which say they are for professional use.
UK officials announced on Sunday that they will roll out 15-minute lateral flow swab tests to all councils and schools in Britain in a bid to get on top of Covid transmitting between people without symptoms.
But one of the main tests being used only detected 41 per cent of Covid cases in a trial in Liverpool where people swabbed themselves, and the manufacturer insists they are only 'intended for use by trained clinical laboratory personnel'.
MailOnline can now reveal that the kits are being bought and repackaged as a self-test by the Government. Ministers have spent more than £825million buying the lateral flow tests from American firm Innova.
Innova says that a medic should use the test on someone with Covid-19 symptoms within five days of those symptoms starting, but the Department of Health is rolling them out for the public to test themselves when they don't have any symptoms at all.
This is despite Public Health England's own study finding the tests are at least 20 per cent less accurate when people do them themselves, and top scientists urging the Government to stop using them, warning they are unfit for purpose as self-tests.
In order to override the original instructions, the Department of Health has listed itself as the manufacturer – despite the fact it plays no part in making the device – so it could have 'flexible' use of the test with the blessing of the regulator, the MHRA.
Scientists described the move as 'bizarre' and warn that the use of low quality rapid testing will potentially give tens of thousands of people a false sense of security by wrongly telling them they are negative when they actually have coronavirus.
Testing experts including Professor Jon Deeks, from the University of Birmingham, have repeated called for the Government to stop using the Innova test – Professor Deeks said today that officials are suggesting to people the test is better than it is.
The team ran data from previous studies on the accuracy of the devices through a simulation to see how many of the PCR-positive tests - which are known to be far more accurate - they would spot.
It found the Chinese made device Orient Gene could detect 90.5 per cent of cases, while the American firm Innova's test spotted 83.7 per cent of infectious people.
Another test, known as the Deep Blue Lateral Flow Assay, was found to be 87 per cent effective.
Professor Peto said: 'Lateral flow tests have been very popular with staff at our hospitals in Oxford, with over 60,000 tests done since November.
'We've been able to detect asymptomatic infected staff who would not have been otherwise diagnosed, protecting patients and staff.
'The tests can be done at home before coming to work with a result available within 30 minutes.'
'We know that lateral flow tests are not perfect, but that doesn't stop them being a game changer for helping to detect large numbers of infectious cases sufficiently rapidly to prevent further onward spread.'
Dr David Eyre, of Oxford's Big Data Institute and Nuffield Department of Population Health, who co-led the study, added: 'When the time comes to relax the current lockdown restrictions, by rapidly identifying the most infectious people using these lateral flow tests, we can potentially relax the lockdown much more safely.
'This would allow people to get back to work, school and their normal activities and still stay safe.'
In a lateral flow test, a swab of the nose or throat is taken and then mixed with fluid that is applied to a piece of absorbent paper that will change colour to indicate whether or not the virus is present, taking just 15 to 30 minutes to produce a result.
Ministers have suggested the tests were a way to help regions come out of tougher lockdowns, enable relatives to visit care home residents and let schools open on time.
But there is fierce debate about whether they are effective enough to allow people to make decisions about their behaviour and movements.
University of Oxford researchers initially found the tests picked up 77 per cent of cases, rising to over 90 per cent of the most infectious.
However, accuracy fell from 79 per cent when used by experts to 58 per cent when carried out by ordinary people without any training.
Real-world testing in Liverpool found the LFDs only picked up 41 per cent of cases when people were using them themselves.
The Scientific Advisory Group for Emergencies (Sage) said last month that lateral flow testing 'should not be seen as a way on its own of enabling high-risk activities to take place, but could reduce the risk of activities that are due to occur anyway'.
Professor Jon Deeks, a testing expert at the University of Birmingham, has accused the Government of making lateral flow tests seem 'better than they are' in a bid to justify the £100billion Operation Moonshot scheme.
Professor Deeks' own study into the reliability of lateral flow tests on students at the University of Birmingham.
Professor Deeks' trial found that the test picked up on only two positive results out of 7,189 people.
To check how well the tests were working, experts at the university retested some of the students using a PCR machine, which is the test used by the Government and is up to 97 per cent accurate. PCR tests are analysed in laboratories and usually take at least a day to return a result.
Retesting around one in 10 of the students in the trial (710 out of 7,189), they found that six of them had wrongly been given negative results and were actually infected.
Multiplying this by 10 to take the whole group size into account suggested as many as 60 cases may have been missed.