Holidaymakers are facing a summer of cancelled flights, with a jet fuel crisis across Europe potentially just six weeks away.

Officials are war-gaming for shortages sparked by the Iran war as early as the late May bank holiday, threatening thousands of families' getaway plans just as the peak season starts.

They are already facing higher fares because the cost of jet fuel has doubled since the conflict started, which airlines are passing on to their customers.

And now travellers could be hit with queues of up to four hours at some European airports, because of new border controls introduced by Brussels.

Yesterday, the head of the global energy watchdog sounded the alarm over jet fuel by saying Europe faces possible shortages in six weeks.

The boss of International Energy Agency (IEA), Fatih Birol, warned that flights may 'soon' start being cancelled if oil supplies remain patchy.

Alluding to the Strait of Hormuz – through which a fifth of the world's oil travels – not yet being fully re-opened, he said: 'I can tell you soon we will hear the news that some of the flights from city A to city B might be cancelled as a result of lack of jet fuel.'

He added that Europe has 'maybe six weeks or so [of] jet fuel left'.

European capitals have been strategising over the potential shortages after the Continent's trade body for airports first warned last week that jet fuel shortages could be just weeks away.

Airports Council International (ACI) Europe said its members had 'increasing concerns' about the availability of jet fuel, warning smaller airports are particularly vulnerable.

And yesterday it emerged UK ministers are war-gaming for potential shortages in around five or six weeks' time.

Officials believe less than 10 per cent of flights would have to be cancelled if shortages hit, because British suppliers have adapted well and 'diversified' where they buy the fuel from.

They have told airlines that they must give passengers at least two-weeks' notice of any cancellations.

However, this could still affect thousands of expectant fliers as the summer holiday high season ramps up.

Airline passengers were left vomiting and passing out after being stranded in an Italian airport on Sunday due to Brussels' new border rules for travellers from non-EU countries, known as the Entry/Exit System (EES).

This automated digital border technology is designed to vet travellers when they arrive and leave.

But there are fears of repeat scenes this summer – and that some European airports will not be able to cope with higher passenger numbers in the peak season, after the system became fully operational last week.

Thomas Reynaert, a Vice President of global industry body IATA, said: 'We are very concerned about the lack of progress in resolving problems with the EES.

'Unless there is action to ensure borders are adequately manned and the electronic gates and remote app are working properly, we could see passengers, including families with kids, queuing up to four hours in popular holiday destinations.'

When asked about the possibility of cancellations because of jet fuel shortages, the Editor of Which? Travel, Rory Boland, said: 'If a package holiday or a flight is cancelled then you should get a refund, although you might lose out if you had a hotel booked separately from the flight.

'It is always safer to book a package, otherwise you are left relying on travel insurance which often has unexpected loopholes.'

Airlines UK, which represents major carriers such as British Airways, easyJet and Ryanair, said: 'We are talking to the Government about crucial measures that will be needed to support aviation in the event of fuel disruption.'

They added that there was 'currently' no disruption to jet fuel supplies.

A Government spokesman said: 'We continue to engage with British airlines to support their operations against the backdrop of war in the Middle East, and to limit the impact on passengers.'

It also emerged yesterday that air ambulances would be prioritised under 'worst case scenario' planning for jet fuel shortages.

According to sources familiar with shortages planning, if our supplies were to completely dry up, emergency services craft – including air ambulances and lifeguard and police helicopters – would be prioritised for receiving the fuel.

But Paul Charles, CEO of luxury travel consultancy The PC Agency, warned: 'Demand to fly is at record highs so it's concerning that airlines may need to pull some flights by the late May bank holiday.

'Even if the war ended tomorrow, there would be a huge fuel gap to fill before new supplies come through. That gap simply can't be filled from other areas... and so it's likely that long-haul flights in particular would be affected quite severely.'

Mr Charles explained: 'Airlines will not be able to guarantee fuel at their destination, so won't be able to fly in, for fear of being stranded.'