Europe's smaller airports are facing an "existential threat", according to the head of the Airports Council of Europe.

Olivier Jankovec, the director general of ACI Europe, has cautioned that some of the continent's smaller airports may not survive if jet fuel shortages sparked by the Middle East crisis result in widespread route cancellations.

Since the Strait of Hormuz was closed during the Iran War, the price of jet fuel has doubled. As a result, numerous airlines have been forced to cancel flights.

Regional airports are most vulnerable to airlines slashing capacity and hiking fares, as demand on their routes is generally more price-sensitive than at larger airports. This comes in the aftermath of the coronavirus pandemic, which has left some regional airports operating 30% below 2019 levels, according to Mr Jankovec.

"The current levels of jet fuel prices and the prospect of a new cost of living crisis mean that many regional airports across our continent are likely to face both a supply and demand shock. For them, this is nothing short of an existential threat," the aviation chief told the Guardian.

By contrast, Europe's largest airports are grappling with an entirely different challenge.

Heathrow, the UK's busiest airport, issued a stark warning regarding its capacity on Wednesday, as the conflict in the Middle East triggered a surge in demand for connecting flights. "Heathrow is full", declared its chief financial officer, Sally Ding. Her remarks accompanied the release of first-quarter figures revealing that 18.9 million passengers passed through the airport during the opening three months of the year — a 3.7% rise compared to the same period last year.

Airspace restrictions arising from the conflict in Iran have prompted an upturn in transfer passengers. This trend is anticipated to continue as geopolitical instability persists, affecting one of the UK airport's principal international rivals for global connections, Dubai.

Heathrow's trading update stated it had "temporarily absorbed demand from elsewhere". It also cautioned that "passenger numbers for the rest of the year are likely to be impacted whilst there is significant uncertainty in the Middle East", as reported by City AM.

Yet as the long-running domestic dispute over planning permission for a third runway rumbles on, Ding warned that Heathrow's operational constraints meant "fewer choices and higher fares for passengers and missed opportunities for the UK economy".

Heathrow's £50bn plan to expand capacity has been mired in political wrangling for years. Its proposals for a new 3.5-kilometre runway would boost passenger capacity to 150m annually, up from the current 84m. This would enable the airport to handle 756,000 flights per year, compared to 480,000 at present. "Our plan is privately financed, rigorously assessed and focused on value. With the right regulatory framework and government policy in place, we are ready to invest, grow and keep the UK connected to the world," a statement from Heathrow said on Wednesday.

The scheme entails reconfiguring part of the M25, London's orbital motorway which runs near Heathrow, by redirecting it through a tunnel. For the first time in Heathrow's history, the Government considered a rival expansion proposal from another company.

The more affordable offer – costing £25bn, and submitted by the Arora Group, which operates hotels and is engaged in property asset management alongside construction – would have bypassed the M25 entirely. It was rejected last autumn by Transport Secretary Heidi Alexander. She chose Heathrow's proposal, though it has encountered additional setbacks following a Government decision to review its wider strategy in its Airports National Policy Statement, now expected this summer.