Public health officials have renewed their criticism of off-the-shelf rapid antigen tests, saying they will not protect people from Covid-19.

"These antigen tests will not keep you safe," National Public Health Emergency Team (Nphet) official Prof Philip Nolan said on Sunday, in a Twitter post.

Harvard epidemiologist Prof Michael Mina, a prominent advocate of antigen testing, responded by claiming Prof Nolan did not appear to know “what you are talking about”.

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“The comment adds nothing of benefit and further sows confusion.”

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Prof Nolan was responding to the promotion of the tests by retailer Lidl, which has begun selling them in packs of five for €24.99.

The supermarket chain's initiative had been criticised by chief medical officer Dr Tony Holohan on Friday, when he said Nphet was "genuinely concerned" about the use of such kits in uncontrolled circumstances.

“Someone could go into the supermarket and buy a pound of sausages and charcoal for a BBQ, as well as a test. That represents a real risk,” according to Dr Holohan.

This prompted Lidl to tweet: “Weekend Super Savers! Pick up a pound of sausages, charcoal for the BBQ and antigen tests for €31”

The retailer admitted it was joking but said it had added antigen tests to its range “to add an extra level of reassurance” to customers as they followed public health advice.

However, Lidl’s tweet prompted a response from Prof Nolan: “Can I get some snake oil with that? It makes for a great salad dressing with a pinch of salt and something acerbic. Stay safe when socialising outdoors over the next few weeks. Small numbers, distance, masks. These antigen tests will not keep you safe”.

The Xiamen Boson Biotech Co, Rapid SARS-CoV-2 Antigen Test card sold by Lidl was one of 16 antigen tests approved in February for use in the EU. It claims to have 93.8 per cent sensitivity (true positives) and 100 per cent specificity (true negatives).

Antigen testing has divided the scientific world, with Nphet and many other national bodies sceptical about the contribution it can make to controlling the spread of infection, particularly when infection rates are low and among people not showing symptoms.

Other experts, in Ireland and other countries, have advocated a greater role for mass, repeated antigen testing to quickly identify cases.

In Ireland, where official use of antigen testing is limited, positive results are confirmed using the standards PCR test.

With antigen tests purchased in retail, consumers swabs their own nostrils while PCR testing is carried out by a health professional.