Stansted Airport has been named the worst in Britain for flight delays.
Planes were on average 25 minutes late compared to 19 at Luton and Birmingham.
Consumer watchdog Which? Travel slammed the inconvenience as “unacceptable”.
The Essex airport is a hub for eastern European airlines and the largest base for Ryanair.
There were eight-minute delays at Belfast City and 13 minutes at Heathrow.
On average flights out of the UK last year were 16 minutes behind schedule, according to analysis of Civil Aviation Authority data by the Press Association.
Liverpool John Lennon Airport, Doncaster Sheffield and Exeter were among the best time keepers of 24 UK airports.
Rory Boland, editor of Which? Travel, said: “These delays can leave holidaymakers hundreds of pounds out of pocket.
“Airlines should introduce automatic compensation.”
London Stansted said: “Ryanair has committed to a multimillion-pound investment to support its ground operation, which has helped deliver significant service improvements to punctuality.”
The Airport Operators Association said delays were caused by factors such as weather and air traffic controller strikes.