Gatwick is reported to be being investigated by the aviation regulator after less than half its flights took off on time during the summer.

The Civil Aviation Authority has started a probe into the reasons for the sharp drop in “on-time performance” at the airport as part of a long-planned review of Gatwick’s regulation, the Sunday Times reported.

Fewer than half of flights took off punctually — defined as within 15 minutes of schedule — during Gatwick’s peak months of June, July and August. Between 51% and 63% of flights landed on time.

The performance is understood to have led to a row between the airport and some of its carriers, of which easyJet is the biggest with 45% of passengers. It could result in Gatwick being forced to compensate airlines, though that is seen as a last resort.

Some airlines are concerned that the airport is pushing too many flights through the world’s busiest single runway. It now handles up to 55 flights an hour and about 43 million passengers a year, up from 50 flights and 31 million passengers in 2009.

However, Gatwick is understood to blame some airlines for scheduling too many flights and using take-off slots inefficiently, as well as strikes by air traffic controllers in Europe.

EasyJet chief executive Carolyn McCall recently urged Gatwick to improve punctuality before adding more flights.

“Infrastructure needs to stabilise for the sake of the airport, passengers and airlines,” she said.

Virgin Atlantic has also complained to the CAA that more flights, poor punctuality and delays to upgrade work are having a “significant impact on resilience at the airport”.

Gatwick is vying with Heathrow to build a new runway for south-east England with a government decision expected as early as tomorrow (Tuesday), the newspaper reported.

A Gatwick spokesman said: “We make sure we meet all our obligations to achieve [on-time performance].

“This year some of our airlines have been affected by weather disruption and air traffic controller strikes in Europe that have made it difficult to meet what are, in some cases, quite ambitious scheduling targets.”

Meanwhile, foreign secretary Boris Johnson has made it clear that he will not resign from the cabinet if a third runway at Heathrow is given the green light.

The former London mayor and now MP for Uxbridge and South Ruislip believes that the government should have an agreed position on future airport capacity and is not looking for a free vote so he can register his opposition.

If his fellow ministers decide to support a new runway at Heathrow rather than expansion at Gatwick, he is expected to accept cabinet collective responsibility, despite previously threatening to lie down in front of the bulldozers, according to the Sunday Times.

However, Willie Walsh, chief executive of British Airways owner International Airlines Group, renewed his opposition to a new runway at Heathrow, describing expansion of the west London hub as a “fantasy project”.

He said: “Recent suggestions that the outrageous £17.6 billion price tag for the third runway could be reduced by £3 billion- £4 billionn merely reinforces our view that this is a fantasy project which has been gold-plated and inflated in an effort to maximise returns for the airport at the expense of our customers and the economy in general.”

It also emerged that Gatwick could build a second runway even if parliament decides Heathrow should expand.