The statement is the latest development in a long-running battle between Ryanair and third-party agents, which the airline says are not authorised to sell its flights.

In the latest warning, Ryanair said an online travel agent, with no affiliation to Ryanair, was offering ‘discounted’ Ryanair flights. But it said no discount existed and that the agent was storing customers’ payment details for fraudulent use at a later date.

It did not name the offending online agent but urged customers to book online via its direct channels, including its website and app.

In November it blamed delayed refunds on unlicensed online travel agents, saying many of these agents “provided false customer contact and fake payment details at the time of booking”.

Ryanair urged customers who “mistakenly booked through an OTA” to check if they had been overcharged using its Price Checker tool and said customers should also look out for its Verified Seal to ensure they had booked directly with the airline.

Dara Brady, Ryanair’s marketing director, said: “This latest OTA scam is yet another reason why passengers should always book direct. Online travel agents are selling our flights but have no commercial agreements with us to do so, and any screen scraping of our website is in breach of the terms of use of www.ryanair.com.”

“In response, we launched the Verified Seal on the Ryanair website and app earlier this year to help customers avoid the pitfalls of booking with online travel agents, who often overcharge, and may provide incorrect customer information which prevents Ryanair from dealing directly with its passengers.

“This was launched in conjunction with our Price Checker tool, in an effort to bring to light the unnecessary mark-ups that online travel agents are charging customers. Over 50,000 customers have used the tool and next time these customers will book directly to avoid being overcharged.”

“Ryanair will continue to raise awareness around the issues associated with OTAs to protect customers from these unlawful practices and we call on consumers to be wary of fake offers of discounted Ryanair flights and to always book directly on the Ryanair.com website/app to access the lowest fares and direct customer care.”