More than a fifth of air travellers who have experienced flight delays in the last two years were held up for more than three hours, according to a Which? Travel survey.
Yet only 38% of them have claimed the compensation to which they were entitled, the poll of 7,729 Which? members found.
The research showed that 37% of the members had suffered a flight delay in the last two years, with 21% being held up for more than three hours.
As many as 44% said they would be happy to pay up to £50 more for a £250 flight if the airline had an excellent rather than average punctuality record.
Separately, Which? Travel analysed Civil Aviation Authority data on flight delays for nine of the busiest UK-operating airlines for the 12 months ending August 2014.
Looking just at arrivals at UK airports, Which? Travel said the figures showed:
:: Twenty per cent of flights failed to arrive within the industry standard of "on time", which is defined as early to 15 minutes late;
:: Flybe was the least delayed of the airlines looked at, with an average delay of 10 minutes;
:: Thomas Cook and Monarch were the only two airlines that failed to meet the on-time standard, with average delays of 18 minutes and 17 minutes respectively;
:: Thomson Airways' average delay was 14 minutes but the airline was responsible for flying seven of the 10 most-delayed routes to the UK from a variety of destinations;
:: Ryanair flew seven out of 10 of the least-delayed routes to the UK, all of which were from European destinations.
The most-delayed route in the 12 months ending August 2014 was a Thomson flight from Orlando's Sanford airport in Florida to Gatwick with an average delay of 68 minutes.
Next was a Jet 2 flight from Chambery in France to Manchester (delayed on average 67 minutes) followed by a Thomson flight from Montego Bay in Jamaica to Gatwick (65 minutes).
Least delayed were a Thomson flight from Marrakesh in Morocco to Birmingham (average delay of less than one minute), a Ryanair service from Sandefjord in Norway to Edinburgh (less than one minute) and a Birmingham-bound service by Monarch from Split in Croatia (one minute on average).
In an additional survey based on the experiences of 11,396 Which? members flying in economy class, Swiss was voted the best short-haul airline with a customer score of 82%, while Thomas Cook came last with a score of 38%.
Singapore topped the table for best long-haul airline with a customer score of 87%, while American Airlines appeared at the bottom of the table with a score of 37%. This survey covered flights in the 12 months ending October 2014.
Which? Travel editor Jill Starley-Grainger said: "Nobody wants to be held up by flight delays so airlines must do everything in their power to ensure they fly on time.
"If you've suffered a flight delay of more than three hours you could be entitled to compensation."
A spokesman for Thomas Cook Airlines said: "While there any many factors that can delay flights - such as weather and strikes - we work hard to ensure our customers depart for their holiday, and return home, on time.
"Unlike some airlines, we never cancel flights and this can skew such figures, but we always ensure our customers reach their holiday destination and look after them during any delays."