Unproven antibody tests put people at risk of contracting coronavirus and spreading it to others, it has been warned.
Experts have urged people against using unapproved kits - designed to detect if someone has had COVID-19 and so may be immune - pointing out no country in the world has yet found a reliable test.
It follows reports of private companies and individuals seeking to buy antibody tests, with the hope of people being able to return to work.
The government is working with several companies that offer the coronavirus tests and is evaluating their effectiveness, but none have yet proved accurate enough to roll out for public use.
Meanwhile, the World Health Organisation has warned there is no evidence that people who have had COVID-19 cannot be infected again.
Professor John Newton, national co-ordinator of the UK coronavirus testing programme, said unverified tests could provide "misleading" results and so pose a danger.
He said: "The government, supported by world-leading experts and regulators, is continuing to work hard to rapidly deliver a reliable and accurate back-to-work antibody testing kit, to counter the spread of the virus and enable people to return to work safely.
"We are breaking new ground with this work every day and I am confident this major research effort will make a breakthrough.
"Until then, please don't buy or take any unproven tests. They may not be reliable for your intended use; they may give a false reading and put you, your family or others at risk."
Prof Newton said securing an accurate antibody test that could reliably be used at home would be "a game-changer".
But he added: "Right now, however, these antibody tests are brand new and still in development.
"No country in the world has yet found an antibody test reliable enough to work as a back-to-work diagnostic, but the UK is leading the way in this emerging area of science and technology, and companies and scientists are doing everything they can to improve the accuracy of the tests on the market.
"As soon we have found a test that works for this purpose, we will be in a position to roll them out across the country as a back to work test.
"In the meantime, I advise organisations, both in the public and private sector, against the use of antibody tests that have not been verified in a laboratory setting: and none have.
"The results of an inaccurate test are potentially misleading and can put people at risk of contracting the disease and transmitting it to others.
"The chief medical officer has also said he strongly discourages the use of unvalidated tests and that, for now, the social distancing guidelines continue apply to everyone."