Experts fear that thousands of Brits may have been told they are coronavirus free because swabs used in tests did not go as deep into the nose as is needed.
The Government has rapidly stepped up testing across the UK and people can now get tested at drive-thrus or have them posted.
But, there are concerns that self-tests are less accurate as they use shorter swabs and do not need to be put as deeply into the nose.
Guidance for the test says: "No force is needed and you do not have to push far into your nostril".
Professional swabs, however, take longer and obtain samples from deep inside the nose, which can be very uncomfortable for some people.
It is this difference that makes infectious disease specialists fearful that self-tests may be producing more false results.
Professor Jon Deeks, a biostatistics expert at Birmingham University, told MailOnline: "A single negative test result doesn’t exclude the disease.
"You can so easily miss the virus – they give a lot of false negatives."
An added issue is that the current guidelines in the UK don’t tell people to stay home after they receive a negative test, even if they have had symptoms.
Dr Andrew Preston, an infectious lung disease expert at the University of Bath, said shallower tests were not as good as professional swabs.
The expert added: "We consider it an unsuccessful swab unless the eyes water. We see real, real issues with the sensitivity of the swab if stabbing in the nose.
"The further back you go, the more chance you’ve got of getting the virus."
It isn’t clear how many tests could have provided false positives, but more than 60,000 are carried out each day in the UK.
The Department of Health also does not release data about false-negative tests.
It comes as Transport Secretary Grant Shapps announced today that face coverings would be made mandatory on public transport from June 15.