Covid-19 antibody tests for NHS and care staff are being rolled out without "adequate assessment", experts warn.

The tests could place an unnecessary burden on the NHS, the 14 senior academics say in a letter in the BMJ,

Last month, the government said it had bought 10 million antibody tests and asked NHS trusts and care homes to make them available to staff in England.

Officials say the blood tests - to see if someone has had the virus - will play an "increasingly important role".

Some patients and people having routine blood tests in England are being offered them too.

What are antibody tests?

They normally show if someone - who has previously been unwell with a bug - has developed antibodies that offer protection against future bouts of the illness.

But how the immune system reacts to the Covid-19 virus remains uncertain.

With the current laboratory tests, NHS England says, a positive result shows a person has had coronavirus.

But crucially, it does not prove they have immunity against future attacks or whether they could transmit the virus to others.

Nevertheless, health officials say gathering the results of these tests will help them understand more about the spread of disease.

What are the concerns?

The group of scientists say as a positive result is unable to prove immunity, the tests offer "no benefit" to hospitals and care staff.

The results do not change what personal protective equipment staff must wear, for example.

The academics also suggest there is little data on how well the test works for people at highest risk - including people belonging to some ethnic minorities and older patients.

Instead, they call for other carefully designed strategies to help monitor the spread of the virus.

What do other experts think?

Prof Sir John Bell from Oxford University, who has advised the government on antibody tests, said the academics who wrote to the BMJ had underestimated the value of the tests.

"We do need to know how many people out there have been infected and the only way to do this is antibody testing," he told BBC Radio 4's Today programme.

But he said they were right to say there was not enough evidence that a positive test indicated immunity. "You couldn't safely use it as a way of telling people whether they could be exposed or not," he said.

Prof Martin Hibberd, of the London School of Hygiene and Tropical Medicine, described the tests as an important component of the public-health response.

He added: "If used successfully, the data generated will be important surveillance information for understanding the effectiveness of control measures put in place."

Meanwhile Dr Tom Wingfield, at the Liverpool School of Tropical Medicine, said he shared the concerns raised in the academics' letter.

He added: "We don't yet have sufficient evidence on accuracy and interpretation of antibody tests."