A fragmented approach to the implementation of the EU’s Digital Covid Certificate across the trading bloc will result in “major operational risks” for airlines and airports and difficulties for passengers, according to an airline lobby group whose members include Ryanair.

The warning comes as latest figures from the Central Statistics Office (CSO) show an uptick in the number of passengers to and from Ireland during May compared with the same month last year.

But the figure is still just a small percentage of the pre-Covid number. Lobby group Airlines4Europe (A4E), whose members also include Aer Lingus owner IAG, EasyJet, Lufthansa and Air France-KLM, has written to heads of state across Europe urging them to harmonise verification standards and protocols for the Covid certificate, “to avoid unnecessary airport queues and ensure a smooth passenger experience”.

The Digital Covid Certificate (DCC) is designed to help get passengers flying again and give airlines some hope that something can be salvaged of the summer season.

The certificate is set to come into use on July 1 across many EU member states, but its introduction in Ireland has been delayed by the Government until July 19.

The certificate is designed to enable anyone who has been vaccinated against Covid, who has recovered from it, or who has recently tested negative, to travel more freely between member states. But it’s still up to individual countries to determine how to treat people in terms of quarantine measures and testing upon arrival.

“While the European Commission has worked closely with industry and delivered in record time the adequate framework allowing for common and fully interoperable DCCs, no less than 10 different national approaches and solutions are currently under review across the EU,” noted A4E.

“Combined with a lack of full and effective integration of the DCC in the passenger journey, as well as duplication of document checks, the current state of play threatens the success of this summer’s air travel restart and will undermine free movement of citizens across the EU,” it claimed.

It noted that the issues have been flagged to the European Commission, which on Monday issued recommendations and guidance to EU countries to address them.

A4E said that average check-in processing times for airline passengers have risen five-fold, to 12 minutes per passenger.

The group told heads of state in its letter that with the peak summer season having arrived, the EU now has a number of tools and measures to enable and support the restarting of air connectivity, travel and tourism.

“We need member states to urgently implement these tools in a harmonised and effective manner,” it said.

“We view these as essential prerequisites to travel, to avoid long passenger queues and waiting times which would create new health hazards and inevitably result in operational issues for airports and airlines.”

CSO data yesterday showed that 85,400 passengers arrived in Ireland by air and sea in May, up 23pc on April. It said 97,000 departed Ireland in May, up 33pc on April.

The figures are still about 95pc lower than pre-pandemic levels.