Air travellers face days of disruption as Heathrow struggles to recover from a fire that shut down Europe’s busiest airport, leading to 1,300 flight cancellations and raising questions about the resilience of the UK’s infrastructure.

The blaze at a local electricity substation caused a power outage that closed the airport in the early hours of Friday morning and forced inbound flights to divert to other hubs, such as Paris and Amsterdam, or return to their original airports.

Some transatlantic flights ended up wherever space was available, including an Air Canada flight from Toronto diverted to Goose Bay, Newfoundland.

At its height, 70 firefighters were tackling the inferno which began shortly before midnight on Thursday and ignited 25,000 litres of cooling oil.

After engineers worked to restore the power supply throughout the day, Heathrow said it would run a handful of flights on Friday evening before fully reopening on Saturday.

A skeleton service of flights resumed just after 7pm, when the first BA plane landed back at Heathrow. 

However, disruption is expected to last for days as carriers began the logistical challenge of restarting their operations with planes, crews and passengers out of place and scattered across the world.

“This is an unprecedented situation, and we have not seen a closure of Heathrow of this scale for many years,” said Sean Doyle, chief executive of British Airways.

London’s Metropolitan Police said its counterterrorism command was leading enquiries, given “the location of the substation and the impact this incident has had on critical national infrastructure”.

On Friday evening the Met added that, while responsibility remained in the hands of counterterrorism police, they were not for the moment treating the incident as suspicious.

“The investigation into the cause of the fire remains in its early stages,” the force said. “After initial assessment, we are not treating this incident as suspicious, although enquiries do remain ongoing.”

The closure following the failure of one local substation also raised questions over Heathrow’s resilience, and whether other parts of the UK’s national infrastructure were similarly vulnerable.

Willie Walsh, a former boss of BA and current head of the International Air Transport Association, criticised what he said was a “clear planning failure” that had left critical infrastructure dependent on a single power source.

Ruth Cadbury MP, chair of the Transport Select Committee, told the BBC the incident “does raise questions about infrastructure resilience”.

Heathrow executives rejected these claims. They said the airport drew power from three substations, as well as backup generators, which offer enough emergency power to keep the runways open although not enough to run the airport’s full operations for an extended period.

Thomas Woldbye, Heathrow’s CEO, said the airport had suffered “an incident of major severity”. He added: “This is unprecedented. It’s never happened before . . . We do not close down the airport unless we have severe safety concerns.”

While only one of the three substations supplying power failed, Heathrow was forced to close down thousands of electrical systems. “Restarting all these systems in a safe way . . . takes a long time”, Woldbye said. “We cannot guard ourselves 100 per cent [against every contingency],” he said.

British Airways, which operates more than half the flights from Heathrow, was by the far the worst affected airline, and told passengers to prepare for long-running disruption.

“This incident will have a substantial impact on our airline and customers for many days to come, with disruption to journeys expected over the coming days,” Doyle said.

The airline had planned to operate more than 670 flights carrying around 107,000 customers on Friday alone, with similar numbers planned over the weekend. More than 200,000 passengers use Heathrow every day.

The complete closure sent passengers scrambling to find other ways to travel. Some airlines, including Ryanair and easyJet, as well as Eurostar’s international train service, put on extra seats to their services, while UK rail operators reported spikes in train bookings.

Some turned to private jets. Toby Edwards, co-CEO of private jet charter company Victor, said demand for flights had “surged”, including one passenger who paid $75,000 to fly across the Atlantic.

As demand soared for rooms hotels near Heathrow were accused of raising prices more than fourfold to as much as £700 per night.

Shares in European airlines closed down on Friday following Heathrow’s closure, including International Airlines Group, the parent of British Airways, which fell nearly 3 per cent.

Additional reporting by Lucy Fisher, Kieran Smith, Akila Quinio and Jamie John