The Government is urging members of the public to stop using coronavirus home testing kits produced by Randox Laboratories.
Health Secretary Matt Hancock said some of the company's kits - which are used in care homes and sent to people at home - are "not up to the usual high standard that we expect."
The Government will be conducting "further testing" of the offending batch "as a precautionary measure."
"While we investigate further, we’re requesting that the use of these Randox swab test kits is paused in all settings until further notice," Hancock added.
But why have the kits been deemed not up to scratch? Here's everything you need to know.
What’s the problem?
The government has not specified the exact issue with the Randox tests, which use swabs to collect samples from the back of the throat and nose.
However, the Department of Health and Social Care said in a statement, "The risk to safety is low and test results from Randox kits are not affected."
There are no reports that any of the kits have caused members of the public harm.
What should I do if I have a Randox kit?
Kits produced by Randox Laboratories are clearly marked with the company's name.
If you have received a Randox testing kit, the advice is to avoid using it until further notice - used kits can still be collected for processing as normal. All other kits provided by NHS Test and Trace can continue to be used for testing.
Who are Randox Laboratories?
Randox Laboratories is a healthcare company based in County Antrim, Northern Ireland.
A £133 million contract to make testing kits for England, Wales and Northern Ireland was reportedly awarded by the government without taking bids from other companies.
In a statement, Randox said the distribution of its tests had been "temporarily suspended" as "an immediate precautionary measure."
The suspension of kits using "one particular batch/supplier of swabs" does not affect test results, it said.