Heathrow saw the equivalent of 40 years of passenger growth in the last four months and admitted service levels “have not been acceptable” recently.
The London hub handled almost six million passengers in June to give a total of 25 million in the first half of the year.
“Unprecedented growth in passenger numbers over the last four months matches what took place over the last 40 years,” Heathrow said.
The airport defended its record in handling flights amid the unprecedented growth.
“We started recruiting back in November last year in anticipation of capacity recovering this summer, and by the end of July we will have as many people working in security as we had pre-pandemic. We have also reopened Terminal 4 to provide more space for passengers.”
But the airport conceded: “Rebuilding capacity quickly is very challenging after the significant reductions in resource across the entire aviation supply chain.
“Arrivals punctuality is very low as a result of delays at other airports and airspace congestion across Europe and this has compounded the challenge of resource constraints for the airport, airlines, ground handlers and government agencies.
“In spite of this, we have been able to provide a good level of service for the vast majority of passengers.
“However, despite our best efforts there have been periods in recent weeks, where service levels have not been acceptable, with long queue times, delays for passengers with reduced mobility, bags not travelling with passengers or arriving late, and we want to apologise to any passengers who have been affected by this.”
A government slot amnesty ended on Friday to encourage airlines to remove summer flights without penalty in a bid to minimise further disruption for passengers over the summer getaway.
The airport said: “Our number one priority at Heathrow is giving passengers a safe and reliable journey. We will carefully assess if airlines’ reviewed schedule changes will help achieve that.”
Heathrow chief executive John Holland-Kaye said: “Last month, we saw exponential growth in passenger numbers as nearly six million people got away – the equivalent of 40 years of growth in just four months.
“I am very proud of the way that our team is rising to the challenge of growth, and giving excellent service to the vast majority of passengers. However, we have already seen times recently when demand exceeds the capacity of the airport, airlines and ground handlers.
“We will review the schedule changes that airlines have submitted in response to the government’s requirement to minimise disruption for passengers this summer and will ask them to take further action if necessary.
“We want everyone who is travelling through Heathrow to be confident that they will have a safe and reliable journey.”