Up to 750,000 unused coronavirus testing kits are being recalled due to safety concerns.
The UK's medicines and healthcare products regulator (MHRA) asked Randox to recall the kits sent out to care homes and individuals.
The government said it was a "precautionary measure" and the risk to safety was low.
It comes weeks after the health secretary said Randox kits should not be used until further notice.
In mid-July, Matt Hancock said the swabs in some kits were "not up to standard".
The Department for Health and Social Care said results from Randox tests were unaffected.
A spokeswoman said: "We have high safety standards for all coronavirus tests. Following the pausing of Randox kits on 15 July, Randox have now recalled all test kits as a precautionary measure."
Care home residents or staff with symptoms of coronavirus can continue to book a test, she said.
Last weekend, a pledge to provide regular testing for care home residents and staff in England was delayed, partly because of the problems with Randox kits.
Healthcare group Randox, based in County Antrim in Northern Ireland, claims to be responsible for up to 17% of the total tests carried out in the UK. About 1.3 million of its tests have been sent out so far.
Around 200,000 coronavirus tests are now being provided across the UK each day.
'Another awkward development'
Problems with Randox tests were flagged up in July, with supplies to care homes and individuals halted.
The Department of Health has stressed that the safety risk is low and recalling the kits is a precautionary measure to remove the possibility of them being used in error.
But this is another awkward development for the test and trace programme in England when it is trying to expand capacity rapidly.
The Randox issue was one factor behind a recent decision to delay a pledge to provide regular testing for care home staff and residents in England.
After questions have been raised about procurement of personal protective equipment (PPE), there will now be more about government contracts for testing provision.