The Chief Medical Officer has said he is "very concerned" about Covid-19 antigen tests that people can buy off the shelves in supermarkets.

Lidl Ireland today began selling tests in stores across the country at a cost of €24.99 for a pack of five.

"As we add these antigen tests to our range, we urge our shoppers to continue to stringently follow the public health advice," the company said on Twitter.

"We hope that by offering them, these tests will add an extra level of reassurance to our customers as they follow that advice."

However, Dr Tony Holohan told a media briefing by the National Public Health Emergency Team that while shops are free to sell what they sell, he believed people are genuinely confused about antigen tests.

He said such tests only have a role to play in "strictly controlled circumstances" where the result is not going to lead to "inappropriate reassurance".

The CMO added that he was "really concerned" that people would feel safe [after getting a negative Covid result using these tests] when they may not be.

He feared they might then undertake activities "they should not be [undertaking] and put people at risk".

The concern was that someone could buy a pound of sausages, charcoal for a barbeque and an antigen test and think "great - [now we] don't have to follow restrictions," Dr Holohan said.

This represents a "real risk to our pandemic response," he added.

The CMO cited the example that if "one person attended a wedding with the disease - in half of circumstances the antigen test will not pick up that case".

There is then a real risk that you get a "super-spreading event".

Dr Holohan said he and his team are "strongly advising people - don't buy these and don't use them".

GP Dr Ray Walley said his practice had seen a case where a person was highly symptomatic but where the antigen test was negative and a PCR test was positive.

Professor Kingston Mills, Professor of Experimental Immunology in Trinity College said he shared some of the CMO's concerns but he said the Department of Health and the HSE needed to embrace the use of antigen testing "stronger than they are".

He told RTÉ's Drivetime that a recent pilot study in meat factories showed a "huge benefit" of rapid antigen testing. However, a study in Britain where people did the tests themselves - outside of a controlled testing - found the results were less accurate.

Meanwhile Leinster Rugby has submitted plans to Government to use rapid antigen testing to allow the return of spectators to matches at the RDS Arena.

Earlier, HSE Chief Executive Paul Reid was asked about the sale of antigen tests in Lidl on RTÉ's Morning Ireland and replied that while antigen tests had a role to play, there was "nothing of higher quality standard than PCR testing. It is well proven".

He advised that if you are symptomatic, seek a GP referral for a PCR test. If you have a positive antigen test "still seek a referral for a PCR test. It is the gold standard."

Also yesterday it was revealed that the Oireachtas Transport and Communications Committee has written to senior Government members and health officials, calling for rapid antigen testing to be used to re-establish air travel.

In their letter, members say that the pilot scheme should be introduced before the European Union's Digital Green Certificate comes into operation.

How do antigen tests work?

According to the HSE, a Covid-19 antigen test uses a swab to take a sample from your nose. The sample does not need to go to a lab. The test results are quicker than the PCR test, but it has some limitations.

The HSE warns that the antigen test is "less accurate than the Covid-19 PCR test.

"The test will find the virus in most people who have symptoms. But in some cases, it may not pick up that you have the virus. If you have Covid-19 symptoms, tell a healthcare worker immediately."

It adds that "no test is 100% accurate. All tests have limitations."

If the result of an antigen test carried out by the HSE is positive (Covid-19 found), you will be told "within one hour of your test and will need to self-isolate".

If your antigen test result is negative or invalid, the HSE will send a second sample to a laboratory for a Covid-19 PCR test.