Half a million coronavirus tests used by thousands of Britons were recalled after spot checks revealed they were not sterile, it was claimed today.
The Department of Health yesterday instructed care homes and the public to stop using the kits produced by Randox Laboratories.
It pulled more than 500,000 of the swab kits amid fears they could give Britons who fear they have the disease unreliable results.
Health bosses have refused to reveal how many Britons used them before they were recalled but the Northern Irish firm is one of the UK's main suppliers of tests.
Early in the crisis, Randox won a £133million contract to carry out at-home Covid-19 tests and ones administered at drive-through centres and care homes.
As part of the deal, swabs are posted to people's houses, care homes and testing facilities and sent back to Randox to be processed in its labs and give a diagnosis.
So tests made by the manufacturer likely account for a huge chunk of the 150,000 swabs being carried out every day in Britain.
Concerns about the safety of the tests were raised on Wednesday when it emerged a Chinese firm which supplies the swabs to Randox had not provided safety assurance documents. This prompted the UK to carry out physical inspections of the kits.
Coronavirus tests made by Randox Laboratories have been retracted over fears they are not safe, it emerged today
A health source told the Sun: 'Spot checks found that swabs in the kit were not sterile. It means samples taken from patients could be contaminated, affecting results.
'Although there is low risk to the public, half a million have been withdrawn as precautionary measure.'
A manufacturer of a high-performing Covid-19 antibody test has still not managed to get it approved by officials for use in England — despite submitting proof months ago that it works better than others on the market.
Derby-based SureScreen Diagnostics first created its rapid antibody test, which tests blood to see whether someone has had Covid-19 already and gives results in just 10 minutes, since March.
Despite repeated attempts to get the test, which looks like a pregnancy test, approved by Public Health England so it could be used in NHS hospitals, the company has still had no success.
But while SureScreen has been waiting, giant pharmaceutical firms from Switzerland and the US have had their tests — which the company claims don't perform as well — approved by PHE and bought in the millions by the Department of Health.
The rapid tests rely on finger-prick blood and are of a type ministers appeared to go cold on after the government wasted in the region of £20million on ones from China that turned out to be no good.
None of the tests — including SureScreen's — have made it through PHE's approval process, with officials focusing instead on lab-based ELISA tests that use blood taken from veins.
Meanwhile the Department of Health has spent millions of pounds on seven different types of lab tests, which most evaluations have shown to be less accurate than SureScreen's test.
David Campbell, director of SureScreen, told MailOnline the company isn't after a major government contract but simply PHE's authorisation to sell its tests, which can be bought privately for £18, to hospitals. In comparison, tests by US company Abbott cost upwards of £45 each online.
Health Secretary Matt Hancock told the House of Commons last night that care homes and testing centres which have stocked up on Randox tests have been told to discard them and they will be sent replacements.
Mr Hancock reiterated that retracting the tests was 'a precautionary step' and that there was 'no evidence' the swabs can cause harm.
He also claimed thousands of Britons who have already taken a Randox test should not worry because it does not affect their results.
The Health Secretary said: 'We've identified some swabs that are not up to the usual high standard that we expect, and we'll be carrying out further testing of this batch as a precautionary measure.
'And while we investigate further, we're requesting that the use of these Randox swab test kits are paused in all settings until further notice.
'Clinical advice is that there is no evidence of any harm, the test results are not affected.
'There is no evidence of issues with any of our other test swabs, and there is no impact on access to testing.'
A Randox spokesperson said: 'As an immediate precautionary measure we have temporarily suspended distribution of home sample collection kits using one particular batch / supplier of swabs.
'This is a temporary measure and does not apply to our private business which uses a different supplier of swabs. Test results from Randox kits are not affected.'
Randox won the second biggest contract for testing in the UK, behind only US-firm Hologic, which secured a £151 million deal.
Randox was awarded the contract by the Department of Health to help make testing kits that the government could use to ramp up its capacity to carry out 100,000 swabs each day back in April.
The Government was criticised for the Randox deal after it came to light that Tory MP Owen Paterson receives a six-figure salary from the firm to act as a consultant.
Randox's tests can produce results in a matter of hours and machines that analyse the swabs can process 54 samples at once.
The Telegraph reports that this is not the first time there have been problems with Randox tests during the UK's fight against Covid-19.
In May, a machine at the firm's lab in County Antrim stopped working and the UK was forced to send tens of thousands of samples to a lab in the US.
But nearly 30,000 of the swabs had to be discarded because they took to long to arrive.
Samples have to be tested within 72 hours of the test being taken, which means that any delay in their processing could leave people with symptoms unsure if they have the virus.