Heathrow has apologised for "unacceptable" flight cancellations, delays and lost baggage which are blighted the return to air travel, but partly blamed other airports and passengers unfamiliar with travelling.
The west London airport said nearly six million passengers travelled through its terminals in June, bringing the total for the year so far to 25 million.
It said the growth in the past four months matches what took place over the past 40 years.
However, the experience for many passengers has been far from enjoyable, resulting in chaotic scenes and great frustration. The airport has previously said the problems could last 18 months.
Today, it was forced to order airlines to cancel 61 flights at short notice as it could not handle the expected number of passengers.
Much of the blame for the months of problems has been placed on the aviation industry for shedding tens of thousands of jobs during the pandemic, then being unable to recruit quickly enough once flights took off again.
However, the industry has also been quick to say that the UK government could have done more to improve the process by speeding up security checks and relaxing rules on '"use it or lose it" routes.
Those regulations have now been eased and the airport urged airlines to take advantage by reorganising schedules to prepare for an “extremely busy summer season”.
A Heathrow statement said: "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."
However, Heathrow did not accept all the blame.
"Many people will not have travelled in some time," the statement said. "Passengers can help prepare for their journeys by ensuring they arrive at Heathrow no earlier than three hours before their flights, that they have their liquids less than 100ml packed in a clear, resealable 1-litre bag and remove their large electronic items from their bags prior to security checkpoints."
Regarding today's cancellations, a spokeswoman for the airport said: “We are expecting higher passenger numbers in terminals three and five today than the airport currently has capacity to serve, and so to maintain a safe operation we have asked some airlines in terminals three and five to remove a combined total of 61 flights from the schedule.
“We apologise for the impact to travel plans and we are working closely with airlines to get affected passengers rebooked onto other flights."
An investigation by PA, meanwhile, showed Heathrow to be Britain’s third-worst airport for flight delays last year. During 2021, the west London airport was found at have had an average flight delay time of 11 minutes and 48 seconds.
Heathrow said it will ask airlines to cancel more flights this summer if it does not believe previous schedule reductions will sufficiently reduce disruption.
Airlines were ordered by the government and the Civil Aviation Authority last month to make sure their timetables are “deliverable” after the sector was unable to cope with demand during the UK's recent jubilee half-term school holiday period.
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.
“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.”
Meanwhile, the boss of a leading airline services company said inaction from ministers Rishi Sunak and Grant Shapps contributed to the “predictable” and “preventable” delays and cancellations that have affected airports across the country.
Philipp Joeinig, chief executive of Menzies Aviation, said requests from the industry for government help in minimising staff shortages fuelled by Brexit and the pandemic have not resulted in “forthcoming” help, exacerbating the current situation.
He said the industry had unsuccessfully lobbied the Treasury earlier in the pandemic, with Mr Sunak then serving as chancellor, for aid after the end of the government’s furlough schemes.
Writing in The Times, he said: “The present travel disruption is not because of a single point of failure, with staffing issues affecting the whole market. Not only was this predictable, it was also preventable.
“Brexit had a big negative impact, reducing the available pool of employees.
“This was compounded during the pandemic, with the British aviation sector suffering huge job losses once furlough schemes ended before the easing of travel restrictions — and with many of these people lost to the industry forever.
“The aviation sector lobbied the government at the time to provide sector-specific aid to retain its skilled, security-cleared people to avoid staff shortages. This was not forthcoming for aviation services businesses.”