Ryanair has responded to threats of legal action from the aviation regulator by emailing customers affected by flight cancellations to clarify their rights.
The airline told passengers they can receive a refund or be transferred on to other flights or travel by trains, buses or car hire.
The Civil Aviation Authority (CAA), which on Thursday accused the Dublin-based carrier of “not complying with the law” over its handling of the fiasco, claimed the airline had “capitulated” after enforcement action was launched.
It had accused Ryanair of not telling passengers that under EU261 rules they were entitled to be re-routed by another carrier.
Ryanair’s offer to passengers features several conditions, including assessing the cost of flights on other airlines “on a case by case basis” before bookings are made.
Alex Neill, a managing director at consumer group Which?, said passengers face a “potential minefield” to reach their destination, describing the process as “convoluted”.
She added: “It still smacks of a lingering reluctance to do the right thing.”
An extra 18,000 flights for the winter season were cancelled by Ryanair on Wednesday – a move that will hit 400,000 customers.
Several popular routes used by UK travellers were hit, such as Stansted to Edinburgh and Glasgow, Gatwick to Belfast, Newcastle to Faro, and Glasgow to Las Palmas.
It adds to mounting anger against Ryanair, which was already coming under heavy fire after cancelling up to 50 flights a day earlier this month.
Passengers have expressed their frustration with the airline, with many left out of pocket due to a lack of alternative flights and accommodation bookings they can no longer use.
Ryanair said the cancellations were brought about because of an error with pilot holiday rosters and insisted the latest reduction in its schedule will “eliminate all risk of further flight cancellations”.
CAA chief executive Andrew Haines said: “Our job is to protect passengers’ rights and ensure that all airlines operating in the UK are fully compliant with important consumer laws.
“Where we find that an airline is systematically flouting these rules, we will not hesitate to take action to minimise the harm and detriment caused to passengers, as we have done with Ryanair in recent days.
“It appears that Ryanair has now capitulated.”
Kenny Jacobs, Ryanair’s chief marketing officer, said: “We apologise again sincerely for the disruption and inconvenience our rostering failure has caused some of our customers.
“We have taken on extra customer service staff and are moving now to process and expedite all EU261 claims from affected customers.
“We are committed to processing all such claims within 21 days of receipt and hope to have all such claims settled before the end of October.”