Around 1.3 million air passengers have suffered severe delays in just 12 months, a study of flight data has revealed.
In total more than 13,000 flights to or from UK airports were delayed by at least three hours in the year to June, consumer group Which? said.
The results show nearly 3,500 passengers faced lengthy delays each day.
Which? found the bulk of the delayed flights were with:
- Easyjet (2,618 flights)
- Ryanair (1,868 flights)
- British Airways (1,668 flights)
But Norwegian, Thomas Cook and and TUI had the highest percentage of severe long-haul flight delays, the report said.
Icelandair, Aurigny, and TUI experienced the highest proportion of severely delayed short-haul flights.
The figures are based on Which? analysis of Civil Aviation Authority punctuality data and cover airlines with at least 1,825 UK flights per year.
Arrivals to the UK from non-European Union based carriers were excluded.
Under EU regulations, passengers are entitled to compensation if they are delayed by more than three hours when flying from the UK or with an EU airline to an EU airport.
If you are delayed for two hours, the airline must offer two free emails or calls, food or drink vouchers as well as accommodation and transfers.
Passengers can claim payouts worth between £220 and £360 for short-haul flights, and up to £535 for longer flights, depending on the length of delay.
Airlines are only exempt from paying compensation if they can prove the delay or cancellation was caused by "extraordinary circumstances" such as extreme weather or airport strikes.
Which? managing director of home products and services Alex Neill said: "Severe delays can be a complete nightmare and totally wreck a long-awaited trip abroad, especially if it means you’re stuck in an airport terminal for hours on end.
"Passengers are often entitled to compensation when airlines get it wrong.
"It is vital automatic compensation is introduced across the industry so that people no longer have to jump through hoops to get what they are owed."
A spokesman for industry body Airlines UK said: "Long delays affect only a minority of overall journeys and are often due to factors outside of an airline’s control.
"When things do go wrong, compensation can easily be claimed directly from an airline when due, and UK airlines have an excellent record of compliance with the rules on compensation and assistance."