The worst offender was Thomas Cook’s Stansted-Dalaman service, with 24% of passengers delayed by more than an hour, increasing to 36% for those travelling in July.

The report says Stansted was the UK’s worst-performing airport for delays in 2018, with more than 10% of flights departing an hour late, and an average delay of nearly half an hour.

Which? added: “High-profile walkouts by Ryanair’s pilots and cabin crew certainly played their part in Stansted’s poor performance. But even if Ryanair flights had been excluded from the analysis, Stansted would still have come out as the worst UK airport for punctuality.”

Liverpool’s Ryanair flight to Milan Malpensa saw 22.4% of flights delayed by an hour or more. It just nudged the next worst offender into third place, a Cook flight from Stansted to Antalya, with 22.2% experiencing delays.

Ryanair passengers experienced the next six worst delays; these were all from Stansted expect one Bristol-Bergamo departure. An easyJet flight from Stansted to Ibiza crept into the top 10, with 18.6% being delayed by more than an hour.

Thomas Cook said it always tried to get passengers to their destination even if this meant long delays and had more reserve aircraft in use this year.

Stansted said punctuality had significantly improved this year, in part because Ryanair had “committed to a multi-million pound investment in additional resourcing and equipment to support ground operation”.