Istanbul airport has overtaken Heathrow as Europe’s busiest hub by passenger numbers, handling 8.15 million travellers in July against 7.9 million at the west London airport, a shift Heathrow says proves its “case for expansion has never been clearer”.

For UK business travellers the change is more than symbolic. Heathrow’s two runways are operating at close to full capacity, which means fuller aircraft, fewer spare slots when disruption strikes and limited room for airlines to add the new routes that corporate flyers increasingly book through rival hubs in the Gulf and Turkey.

How Istanbul pulled ahead

Figures published on Tuesday showed Heathrow’s July passenger total fell 1.5% compared with the same month last year, partly due to the war on Iran, while the Turkish hub recorded a 2.3% increase. Heathrow had already trimmed its passenger and profit forecasts for the year, blaming the conflict in the Middle East for softer demand.

For more than two decades before the pandemic, Heathrow served more passengers than any other European airport, according to annual figures from the trade body Airports Council International. It lost that position in 2020 amid coronavirus travel restrictions before regaining it in 2023.

The comparison with Istanbul is not entirely like for like. The Turkish airport only opened in late 2018, was built on a new site away from the city and residential neighbourhoods, has a vastly bigger footprint and can operate around the clock. Its position near the Gulf, now the crossroads of international air travel, has also fuelled its growth.

Istanbul airport’s chief executive, Selahattin Bilgen, called the milestone significant. “Thanks to our three independent runways, which can be operated simultaneously 24 hours a day, our advanced operational capabilities and high capacity, we have successfully overcome the capacity constraints faced by many major global hub airports,” he said. A fourth runway is set to become operational by the end of this year.

What it means for the third runway debate

Heathrow is seeking government permission to build a third runway, with a £33bn expansion plan that would allow it to accommodate 150 million passengers a year. The airport said: “The case for expansion has never been clearer, as Heathrow was overtaken in July by Istanbul airport as the busiest hub in Europe. Our plans will ensure the country gets the infrastructure it needs to stay competitive and will deliver all-important economic growth.”

The transport secretary, Heidi Alexander, launched a consultation on the Heathrow expansion national policy statement in June, setting out the conditions for the third runway to go ahead. The then chancellor, Rachel Reeves, said at the time she was determined to get “spades in the ground” in the current parliament, with the runway built by 2035. Airlines, however, have demanded a review of Heathrow’s costs before any approval, and Greater Manchester’s mayor, Andy Burnham, has argued the plans divert infrastructure investment “away from the north and traps it in London”.

Heathrow’s chief executive, Thomas Woldbye, said: “Expanding Heathrow will help ensure the UK remains home to Europe’s leading hub and continues to benefit from the trade, investment and tourism that increased connectivity will bring.”

Records elsewhere in the UK

While Heathrow slipped back, other UK airports posted their best ever July figures. London Stansted welcomed 3.1 million passengers, its busiest month on record and a 6.3% increase year on year, while Manchester served 3.4 million.

For business travellers weighing up their options through the London hub this autumn, our guide to navigating Heathrow covers terminals, lounges and transfer times in detail.