Acknowledging an "unacceptable increase in delays" during the holiday season, the airport said the biggest change since restrictions were lifted was that leisure rather than business travellers were now the majority of passengers at Heathrow.
It said that holidaymakers "often travel with more luggage and are less familiar with travel rules which can slow their progress through the airport, particularly at check-in and security checkpoints".
Passengers have spent about 35,000 extra hours in security because liquids were left in hand luggage rather than placed in a clear bag. This then had to be inspected by airport staff, the airport said.
"Heathrow data shows that at least 60 per cent of bags rejected at security checkpoints are subjected to time-consuming hand searches because passengers haven’t removed all of their liquids from bags before screening," it said.
"Even now, when all security lanes are open and fully resourced, these additional checks slow down the flow through security for all passengers."
Passengers can bring liquids up to only 100 millilitres in their hand luggage for security reasons. The restriction was brought in after a foiled 2006 terror plot involving liquid explosives and has never been repealed.
Decades of flight: Heathrow Airport - in pictures
Business travel has been slow to recover after the pandemic brought about lasting changes to work habits, and analysts have said it is still some way off exceeding pre-pandemic levels.
In leisure travel, Heathrow, Britain's busiest airport, said the school summer holidays "off to a strong start" as a million people departed in the space of 10 days, the busiest such period since Christmas 2019. New York, Los Angeles and Dubai were the top destinations.
But the industry's comeback has been marred by long queues, baggage problems and cancelled flights that have damaged Heathrow's reputation and frustrated passengers at other British airports.
The London airport in July introduced a 100,000-person-a-day cap on travellers — which the new figures would suggest has been hit ― and told airlines to adjust their schedules. The problems led on Tuesday to British Airways suspending sales of short-haul flights from Heathrow.
Heathrow said it had hired more than 1,300 new staff since November and that it was airlines who had failed to fill enough positions to cope with recovering demand.
"Although they may sometimes take slightly longer to check passengers than their more experienced colleagues, they are becoming more efficient with each passing week as they gain valuable experience," it said of its new security staff.
The airport's chief executive John Holland-Kaye said last week that the delays were partly due to people not "checking in all of their make-up" before going through security.
He offered another explanation for hold-ups: that some passengers were imitating what he said was a TikTok trend in which they would falsely pose as disabled passengers so they could be wheeled through the airport.
"If you go on TikTok, you’ll see that that is one of the travel hacks that people are recommending. Please don’t do that," he told LBC radio.