The Civil Aviation Authority (CAA) said the Irish budget airline was failing to treat people with transparency and fairness, The Times reports.

In particular, it was critical of excessive fees imposed by the carrier for transferring tickets to other people, fixing spelling mistakes and checking in at airports.

While other carriers were criticised, Ryanair and Hungarian budget airline Wizz Air, received particular criticism.

The CAA found that Ryanair charged £55 to check in at the airport and £25 to print out a boarding pass there.

The airline was told that if it fails to review its fees, this “could provide the basis for legal challenge” by passengers under consumer protection law.

The findings come in a review conducted over two years of terms and conditions imposed by 14 airlines.

The CAA, which surveyed more than 1,000 passengers, said almost four in 10 people failed to read ticket rules when booking.

Paul Smith, the CAA’s consumer director, said: “Consumers often do not read their airlines’ terms and conditions. It has therefore been important for us to review this area and work with the industry to seek positive changes.”