The promise of 100,000 daily coronavirus tests by the end of the month is in huge doubt, with a warning that the technology will not be ready by then.

But an Oxford University professor advising ministers has warned that none of the antibody tests – to find out if someone has had the virus and recovered – is yet working properly.

Without mass antibody tests, it will be very difficult to achieve the 100,000 commitment, given the problems securing sufficient chemicals and swabs for antigen tests, which show if someone currently has the virus.

Although some progress is being made, only around 16,000 of those tests were carried out on Sunday – and only around 1,000 on NHS staff and their families at the new drive-through sites.

There has been speculation that Mr Hancock might be forced to resign if the target has not been reached by end of April, little more than three weeks away.

Writing on his blog, Professor Sir John Bell, regius professor of medicine, said: “Sadly, the tests we have looked at to date have not performed well.

“We see many false negatives (tests where no antibody is detected despite the fact we know it is there) and we also see false positives.

“None of the tests we have validated would meet the criteria for a good test as agreed with the Medicines and Healthcare Products Regulatory Agency (MHRA). This is not a good result for test suppliers or for us.”

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Sir John said the Spanish government had also returned test kits that were not working, while Germany believed it was “three months away from getting these available”.

“We clearly want to avoid telling people they are immune when they are not, and we want all people who are immune to know accurately so they can get back to work,” he added.

When Mr Hancock made his pledge – saying “that is the goal and I am determined that we will get there” – he declined to say how many would be antigen tests and how many for antibodies.

However, it is widely accepted that ministers waited too long before ordering antigen tests and so have staked their hopes on checking accurately for antibodies as the only “exit strategy” from the crisis.

They have floated the idea of immunity certificates for people able to prove they can safely escape the lockdown early, in the months to come.

It is believed that tests ordered from China were able to identify immunity accurately only in people who had been severely ill, when the UK needed to identify milder cases as well.

Asked about the situation, Boris Johnson’s spokesperson confirmed: “No test so far has proved to be good enough to use.”