Heathrow Airport warned of "big challenges" across aviation as disruption from the war in Iran continued to weigh on passenger numbers over the summer.
The west London airport said 7.87 million passengers passed through its four terminals last month, a 2.1 per cent fall compared with the same period last year.
That came despite Heathrow recording its "busiest ever day" on 2 August, when nearly 272,000 passengers passed through the airport.
The decline followed a 1.5 per cent fall in passenger numbers in July, when Heathrow lost its position as Europe's busiest airport to Istanbul. Heathrow held the top spot between 1996 and 2019, before losing the title during the pandemic and reclaiming it in 2023.

Punctuality record holds up
Heathrow said that despite the disruption, passengers had consistently smooth journeys. It said 98 per cent of passengers waited less than five minutes at security, and 98 per cent saw their bags depart as planned, helping the airport retain its title as Europe's most punctual hub.
Technical fault triggers mass cancellations
The fall in passengers over Heathrow's peak summer period came before widespread cancellations this week, after a technical issue at National Air Traffic Services, the body that manages air traffic control across UK airspace, struck on Tuesday.
Airlines were forced to cancel more than 2,000 flights arriving in or departing from the UK, adding to disruption across the aviation industry since the start of the year.
Fewer UK, EU and Middle East passengers
Customers had already pulled back from booking trips over the summer. Heathrow recorded a 1.7 per cent drop in passengers travelling from the UK last month, ahead of a 0.3 per cent fall in passengers from the European Union.
The airport reported a near 20 per cent fall in passengers from the Middle East last month, as the war continues to disrupt travel to and from the region.
Renewed push for a third runway
Heathrow's chief executive, Thomas Woldbye, repeated calls for the Government to approve a third runway at the airport, arguing that growth is being held back without it.
"This summer Heathrow remained Europe's most punctual hub," Woldbye said. "The longest queue at Heathrow is now the one made up of over 40 airlines that want to better connect the UK but can't secure a slot because our runways are full."
"Expansion is a national project that will create jobs, unlock growth and make travel more affordable," he said.
Chancellor John Healey told Treasury Questions in the House of Commons on Tuesday: "After years of delay, years of indecision, years of often vexatious challenge, we have given the go-ahead to this project quite simply because the economic case stacks up and will help bring growth."

