Flight punctuality at Heathrow declined sharply in the three months to June, highlighting the strain on capacity at the airport.

Civil Aviation Authority (CAA) figures show Heathrow had the worst on-time performance for scheduled flights at the UK’s 10 biggest airports in the second quarter of the year.

More significantly, the CAA recorded a six percentage point rise year on year to 27% in the proportion of flights delayed at Heathrow.

That compared with delays to 22% of scheduled flights across the 10 airports during the second quarter – or, as the CAA puts it, 78% of arrivals and departures were on time.

A flight is considered on time if it is no more than 15 minutes late arriving or departing. Heathrow recorded 73% of flights on time.

Overall, the punctuality of scheduled flights fell by two percentage points.

London’s airports showed a 77% on-time performance and two-minute increase in average delay to 13 minutes year on year.

Punctuality at Gatwick declined by three percentage points, there was a two percentage point fall at Stansted and one percentage point decline at London City. Luton’s performance improved by one point.

Manchester, Birmingham, Glasgow and Edinburgh also showed declines in scheduled flight punctuality.

However, charter punctuality improved year on year rising from 75% to 77%. The average charter delay, which is usually longer than the scheduled average, also improved from 20 minutes to 17 minutes year on year.

Part of the reason could be a near 13% fall in the number of charter flights over the same period in 2011. By contrast, there was a 0.8% increase in scheduled flights.

The average delay for all UK flights increased by one minute to 12 minutes compared with the same period last year.

Flights to and from Toronto recorded the worst on-time performance (52%) of the 75 busiest scheduled routes and the highest average delay (28 minutes). Those to Rotterdam achieved the best punctuality, with 94% on time.

CAA regulatory policy group director Iain Osborne said: “The drop in performance for scheduled flights is a warning sign. We urge airports, airlines and air traffic control to work together to reverse this trend and reduce delays.”