"In one case a test that I'm being urged to buy missed three out of four positive cases for coronavirus".
He said the United Kingdom would hit 100,000 tests a day, which can be made up of antigen tests that show whether people are now suffering from Covid-19, as well as antibody tests to see whether people have had the infection and have recovered.
Addressing a press conference at Downing Street, he spoke about testing kits and plans to combat coronavirus.
Mr Hancock said it is "frustrating" the first antibody tests to undergo testing have not worked, but more are coming, with many produced in China and some domestically.
"That is an important thing that we will be doing and are looking at, but it's too early in the science to be able to put clarity around that".
The UK has ordered several antibody tests but so far they have been said to be ineffective. "But we hope the later tests we have got are reliable enough for people to be confident in using".
However, coronavirus testing has so far had mixed success around the world.
In an unusually detailed statement, the secretary, who had just ended his seven-day self-isolation after testing positive for coronavirus, shared details on what that strategy will look like.
It is known that COVID-19, the respiratory disease caused by the coronavirus, develops an immunity in recovered patients, but there's no evidence to suggest how long this protection lasts.
On Friday, he said now no antibody tests have been "pencilled in" as part of the 100,000 figure, and said it was likely most of the target would be made up of the diagnostic swab tests.
If the project is approved, the researchers will test 100,000 people at a time starting this month, Der Spiegel said.
It is not yet known if the antibodies will mean a person is permanently immune from COVID-19 or if it is only short term if the virus mutates.
So far, 163,194 people in the United Kingdom have been tested for Covid-19 - roughly 0.2% of the population. Volunteers are asked by Global Positioning System if they want to take part, and Prof Van Tam praised the "fantastic work by both clinicians and by patients".
Germany has one of the lowest COVID-19 death rates, which some experts and commentators have said is a result of the extensive testing rolled out by Chancellor Angela Merkel's government.