Aviation regulators have raised questions over queue monitoring procedures at Gatwick and Heathrow airports.
The Civil Aviation Authority (CAA) commissioned month-long checks at the two airports this summer, with the findings revealing that security queues were longer than had been reported in past months.
The airports have agreed to increase efforts to improve the situation after the CAA wrote to them in the wake of the findings.
The CAA report found that many passengers spent longer than five minutes queuing at Heathrow’s Terminal 5 in July.
A penalty payment totalling £500,000 was paid to airlines in the wake of the report. It was the first such fine at the airport since the Big Freeze crippled transport networks last Christmas.
At Heathrow “the queue profile visibly differed between when the auditors were present and the profile in previous months”, according to the authority.
At Gatwick, an audit of its north terminal in July also showed that the queue profile differed compared to past months.
CAA regulatory policy director Iain Osborne suggested the findings would help boost the quality of queue monitoring in the future.
He added: “We are ensuring that the UK’s two largest airports’ measurement of their security queue performance is of the highest possible standard.
“We welcome the airports’ agreement to the steps we consider necessary in light of the audit to ensure the data is beyond reproach.
“This will reinforce the confidence the travelling public can have in these measures, expressly designed to improve the passenger experience.”
Meanwhile, separate figures showed that Gatwick Airport has revised down its forecast for passenger numbers over the next 10 years.
Previous estimates had totalled the annual number of fliers by 2017 at 40 million. However, the airport has said that it will take until 2020 for that target to be realised.
The airport reported that traffic growth was “lower than previously disclosed”. It said that this aligned with the current state of the economy.
However the airport – owned by US fund Global Infrastructure Partners – said that in fewer than 20 years it could handle around 45 million passengers on one runway with two terminals.
Last month saw passenger traffic rise 4.9 per cent, compared to just 1.4 per cent of growth at the BAA-owned Heathrow.