LONDON — On-time performance at UK’s airports has fallen to its lowest level in five years.

Strong growth in passenger and commercial flight numbers have been accompanied by a reduction in on-time performance for scheduled passenger flights, said the UK’s Civil Aviation Authority.

In Q3 2015, on-time performance fell by three percentage points, from 76% to 73% across 24 airports when compared with Q3 2014.

London airports dropped from 73% in Q3 2014 to 69% in Q3 2015. Regional airports dropped from 80% to 77%. The average delay per flight across the 24 monitored airports was 15 minutes for Q3 2015.

According to TravelMole, the average delay at London Gatwick was the worst, averaging 23 minutes. The average delay at London Heathrow was 15 minutes and at London Stansted, 12 minutes.

“Airlines are accommodating the continuing strong passenger demand by carrying the extra passengers on larger aircraft, rather than increasing the number of flights significantly. However, punctuality was the worst of any summer period since 2010 – something we know many passengers will have found frustrating and an issue airlines, airports and air traffic control services should work to address,” said Tim Johnson, CAA Policy Director.

“The strong passenger demand and a drop in punctuality also underlines the importance of addressing the ongoing pressures on runway capacity in the South East and the need to modernize the UK’s airspace.”

The country’s airports saw their busiest summer ever between July and September 2015 as the number of passengers passing through UK airport terminals hit a new peak of over 78 million, according to the CAA’s latest Aviation Trends report. Rolling 12 month passenger totals passed 250 million for the first time ever.

UK airport terminals handled more than 78 million passengers, making this the strongest Q3 ever recorded and representing a 5.5% rise from the 74 million passengers recorded in Q3 2014.