Almost a quarter of the 1.9 million flights to and from the UK in the 11 months to March are reported to have been delayed by 15 minutes or more.

The delays to 449,000 flights disrupted the journeys of 43 million people. More than 10,000 were over three hours late, according to the consumer group Which?

It reported that up to a million passengers were potentially in line for compensation under the EU Denied Boarding Regulation, which allows claims of up to €600 depending on the circumstances of the delay.

Which? found that Southend was the airport where passengers were most likely to be delayed on short-haul flights. Gatwick and Manchester suffered the most delays to long haul journeys.

Vueling, Loganair and Aurigny had the highest percentage of delays of three hours or more to short haul flights.

Passengers travelling with Pakistan International Airlines, Air India and US Airways were most likely to face three-hour delays on long haul flights. The average delay for a PIA flight was nearly 45 minutes.

Emirates, Etihad, Jet Airways and Singapore Airlines had the lowest number of delays in the long-haul sector.

Which? encouraged passengers to claim compensation but warned that where flights were delayed because of factors such as extreme weather or airport strikes, airlines were exempt from payouts.

Director of policy and campaigns, Alex Neill, told The Times: “Arriving at the airport to discover your flight has been delayed is incredibly frustrating, and something thousands of holidaymakers will encounter this summer.

“We know that tens of thousands of passengers on late running flights are not claiming the compensation they’re due and so we encourage people to claim what they’re rightly entitled to.”

The organisation said that compensation was dependent on the length of delay and how far the passenger was travelling.

Long-haul travellers were entitled to €300 (about £250) if their aircraft landed between three or four hours late, or €600 if their flight was at least four hours behind schedule.

Its analysis showed that 183,000 long haul passenger journeys were delayed by at least three hours.

Passengers flying short haul were potentially eligible to claim up to €250 if they were delayed by more than three hours. Which? said that 729,000 short- haul passenger journeys were affected by such a delay in the 11 months to March.

Passengers can claim compensation if they are travelling to or from an EU airport, on an airline based in the EU.

Whether Britain is included in the regulations in future will depend on the Brexit deal that is negotiated.

*Average delay; percentage of flights delayed more than 3 hours:

Worst airlines

Short haul

Vueling 24.6 minutes; 1.9%

Loganair 19.6 minutes; 1.6%

Aurigny 17 minutes; 1.3%

Long haul

Pakistan International Airlines 44.5 minutes; 4.2%

Air India 26.8 minutes; 3.7%

US Airways 23.8 minutes; 2.1%

Worst airports

Short haul

Southend 15.6 minutes; 1.7%

Gatwick 18.8 minutes; 0.8%

Cardiff 13.8 minutes; 0.7%

Long haul

Gatwick 21.7 minutes 1.3%

Manchester 19.2 minutes; 1.3%

Birmingham 17.5 minutes; 1.2%