Heathrow Airport has asked airlines to stop selling summer tickets as the aviation sector struggles to deal with demand for travel.
The extraordinary move has seen the airport introduce a capacity cap of 100,000 daily departing passengers until September 11.
Heathrow’s chief executive John Holland-Kaye said it could handle around 100,000 departing seats a day, but forecasting predicted daily departing seats over the summer will average 104,000 seats.
About 1,500 of those 4,000 extra seats above capacity had already been sold to passengers, so the airport was asking airlines to stop selling more summer tickets.
The measures had been taken because some airlines had not taken enough action to reduce their schedule, despite an ‘amnesty’ by ministers to remove slots from schedules without penalty in a bid to cope with demand on airports.
He said: "Over the past few weeks, as departing passenger numbers have regularly exceeded 100,000 a day, we have started to see periods when service drops to a level that is not acceptable: long queue times, delays for passengers requiring assistance, bags not travelling with passengers or arriving late, low punctuality and last-minute cancellations.
"This is due to a combination of reduced arrivals punctuality (as a result of delays at other airports and in European airspace) and increased passenger numbers starting to exceed the combined capacity of airlines, airline ground handlers and the airport.
"Our colleagues are going above and beyond to get as many passengers away as possible, but we cannot put them at risk for their own safety and wellbeing."
Officials at BA, one of the major airlines operating from Heathrow, were locked in meetings on Tuesday to discuss how to respond.
Mr Holland-Kaye said that a significant factor in the constraint on passenger numbers was a lack of ground staff, who are contracted by airlines to provide check-in staff, load and unload bags and turnaround aircraft.
The airport boss apologised for the impact the capacity cap would have on holidaymakers, with the capacity cap covering the summer holidays.
“By making this intervention now, our objective is to protect flights for the vast majority of passengers at Heathrow this summer and to give confidence that everyone who does travel through the airport will have a safe and reliable journey and arrive at their destination with their bags,” he said.
“We recognise that this will mean some summer journeys will either be moved to another day, another airport or be cancelled and we apologise to those whose travel plans are affected.”
It comes after months of travel disruption in airports across the UK, with Heathrow officials saying it had seen 40 years of passenger growth in just four months.
On Monday morning, Heathrow ordered the cancellation of around 60 morning flights in bid to cope with demand, affecting the travel plans of around 10,000 passengers.