A review by the authority of the 30 largest airlines operating across the EU found that although most were able to demonstrate they could offer passengers a replacement flight on another airline, it was “not made sufficiently clear” to consumers when or how this would take place.

The CAA said it had found a “varied picture” around certain airlines’ rerouting policies and the options they provided to consumers who needed to use the service.

It has given carriers until June 30 next year to make adjustments to systems and processes.

Under Article 8 of EU261/2004, passengers have the right to be re-booked on an alternative flight if their original flight has been cancelled, even if the flight is with a different airline.

The CAA said “most airlines” demonstrated to passengers that they could be flown on other airlines but offered “little clarity over the circumstances in which this option would be taken up”.

The authority also highlighted “in particular, [the] little clarity” to travellers that they may be entitled to be flown on another airline.

Paul Smith, group director, consumers and markets, said: “We expect airlines to work towards making the necessary adjustments straight away. We appreciate it may take some time, in terms of IT systems and to train frontline staff and update passenger information.

"We will take account of this when deciding how to use our enforcement powers.”

In a letter to airlines, Smith said the CAA recognised there were times when rerouting “meant the benefit to consumers was outweighed by the cost to the airline” and sometimes as a result, passengers arrived at their destination only slightly earlier with a different carrier’s next available flight than they would have done had they been rerouted on the original carrier’s next available service.