Analysis of more than 850,000 inbound flights revealed that 26% failed to arrive within 15 minutes of their schedule last year.
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Canadian leisure airline Air Transat was the worst performer with 45% of its flights late, followed by Icelandair (44%) and Norwegian (40%).
Delayed passengers may be able to claim compensation under EU law, but if the disruption is caused by factors such as extreme weather or airport strikes they are unlikely to receive a payout.
KLM was found to be the most punctual airport in 2016 with just 12% of flights late.
Which? claims passengers making complaints against airlines are poorly served and has called for the next government to introduce a transport ombudsman that all airlines must join to improve the way grievances are dealt with.
The organisation's magazine editor, Richard Headland, said: "Flight delays are one of the most annoying things about travelling. These figures show just how frequently flights fail to reach their destination on time.
"If you're unlucky enough to experience a severe delay, compensation is available and people should claim what they're rightly entitled to.
"We know that resolving complaints with airlines can be a very tricky process, so we're calling on the next government to legislate for a new, mandatory transport ombudsman."