The British government has ordered an investigation into the country's “energy resilience” after an electrical substation fire shut Heathrow Airport for almost a day and raised concerns about the United Kingdom's ability to withstand disasters or attacks on critical infrastructure.

While Heathrow Airport said it was now “fully operational”, thousands of passengers remained stuck, and airlines warned that severe disruption will last for days as they scramble to relocate planes and crews and get travellers to their destinations.

Inconvenienced passengers, angry airlines and concerned politicians all want answers about how one seemingly accidental fire could shut down Europe’s busiest air hub.

“This is a huge embarrassment for Heathrow airport," said Toby Harris, a Labour MP who heads the National Preparedness Commission, a group that campaigns to improve resilience.

"It’s a huge embarrassment for the country that a fire in one electricity substation can have such a devastating effect."

Global airlines land at Heathrow after airport resumes operations. – Reuters/Focus 365

Energy Secretary Ed Miliband said he'd asked the National Energy System Operator, which oversees UK gas and electricity networks, to "urgently investigate" the fire, “to understand any wider lessons to be learned on energy resilience for critical national infrastructure."

It is expected to report initial findings within six weeks.

“The government is determined to do everything it can to prevent a repeat of what happened at Heathrow," Miliband said.

Heathrow announced its own review, to be led by former transport secretary Ruth Kelly, a member of the airport's board.

Heathrow Chairman Paul Deighton said Kelly will look at “the robustness and execution of Heathrow’s crisis management plans, the airport’s response during the incident and how the airport recovered.”

More than 1300 flights were cancelled and some 200,000 people stranded on Friday after an overnight fire at a substation 2 miles (3.2km) away from the airport cut power to Heathrow, and to more than 60,000 properties.

Heathrow said it had “added flights to today’s schedule to facilitate an extra 10,000 passengers".

British Airways, Heathrow’s biggest airline, said it expected to operate about 85 per cent of its 600 scheduled flights at the airport on Saturday.

Heathrow closure 'unprecedented' says British Airways chief. – Reuters

While many passengers managed to resume stalled journeys, others remained in limbo.

Laura Fritschie from Kansas City was on vacation with her family in Ireland when she learned that her father had died.

This weekend she was stranded at Heathrow after her BA flight to Chicago was cancelled at the last minute.

“I’m very frustrated," she said. “This was my first big vacation with my kids since my husband died, and ... now this. So I just want to go home.”

Heathrow outage leaves passengers stranded overnight in Atlanta. – AP

Residents in west London described hearing a large explosion and then seeing a fireball and clouds of smoke when the blaze ripped through the substation.

The fire was brought under control after seven hours, but the airport was shut for almost 18 hours. A handful of flights took off and landed late Friday.

Police said they do not consider the fire suspicious, and the London Fire Brigade said its investigation would focus on the electrical distribution equipment at the substation.

Still, the huge impact of the fire left authorities facing questions about Britain’s creaking infrastructure, much of which has been privatised since the 1980s.

The centre-left Labour government has vowed to improve the United Kingdom's delay-plagued railways, its aged water system and – especially – its energy network, promising to reduce carbon emissions and increase energy independence through investment in wind and other renewable power sources.

“The last 40, 50 years we’ve tried to make services more efficient,” said Harris. “We’ve stripped out redundancy, we’ve simplified processes.

"We’ve moved towards a sort of ‘just in time’ economy. There is an element where you have to make sure you’re available for ‘just in case’. You have to plan for things going wrong.”

Heathrow is one of the world’s busiest airports for international travel, and saw 83.9 million passengers last year.

Chief executive Thomas Woldbye said he was “proud” of the way airport and airline staff had responded.

“The airport didn’t shut for days. We shut for hours,” he said.

Woldbye said Heathrow's backup power supply, designed for emergencies, worked as expected, but it wasn’t enough to run the whole airport, which uses as much energy as a small city.

“That’s how most airports operate," said Woldbye, who insisted “the same would happen in other airports" faced with a similar blaze.

But Willie Walsh, who heads aviation trade organisation IATA, said the episode “begs some serious questions”.

“How is it that critical infrastructure – of national and global importance – is totally dependent on a single power source without an alternative? If that is the case, as it seems, then it is a clear planning failure by the airport,” he said.

Walsh said “Heathrow has very little incentive to improve” because airlines, not the airport, have to pay the cost of looking after disrupted passengers.

What happens for passengers after Heathrow Airport shutdown? UK travel expert explains. – AP 

Friday’s disruption was one of the most serious since the 2010 eruption of Iceland’s Eyjafjallajokull volcano, which shut Europe’s airspace for days.

Passengers on about 120 flights were in the air when the closing was announced and found themselves landing in different cities, and even different countries.

Mark Doherty and his wife were halfway across the Atlantic when the inflight map showed their flight from New York’s John F. Kennedy Airport to Heathrow was turning around.

“I was like, you’re joking,” Doherty said before the pilot told passengers they were heading back to New York.

Doherty called the situation “typical England — got no back-up plan for something happens like this. There’s no contingency plan.”

Heathrow Airport in numbers

• Heathrow serves more than 230 destinations in nearly 90 countries.
• 90 airlines have made Heathrow their base, including British Airways, Virgin Atlantic and Lufthansa.
• There are two main runways. The northern one is 3902 metres long. The southern is 3658 metres.
• The airport will submit its proposal for a third runway this summer, weeks after the British government granted its support to the project citing its potential to boost trade and economic growth.
• According to the group's traffic summary, 5.7 million passengers travelled through Heathrow in February 2025, making it the busiest February on record. Passenger numbers amounted to 84.1 million from March 2024 to February 2025.
• Heathrow is operating at 99 per cent capacity and risks being overtaken by European rivals. Its two runways compare with four each at Paris' Charles de Gaulle and Frankfurt Airport, and six at Amsterdam's Schiphol.
• There are around 475,000 total aircraft movements annually.
• The most popular destination is New York.
• Over 90,000 people work at the airport, the UK's largest single-site employer.