Tests recently went on sale at Lidl.
The World Health Organisation says people could be making "inappropriate decisions" if they rely on the result from an antigen test.
The tests, which recently went on sale in Lidl, get a result quicker - but aren't as accurate as other types such as PCR.
The Chief Medical Officer has strongly recommended against people buying and using antigen tests themselves.
Dr Margaret Harris from the WHO says people could get false reassurance from the result:
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The World Health Organisation says antigen tests are a useful tool that can be used in some settings.
Dr Harris says they can play a role in some instances: