Mayor of London Sadiq Khan has urged passengers to check with their airlines before making their way to Heathrow.

He posted on X: “Flights have resumed at Heathrow following yesterday’s power outage.

“Operations are returning to normal. I know this has been frustrating, and I want to thank emergency services, Heathrow staff, and engineers for their efforts.

Power supplies have been restored to all customers connected to National Grid UK’s North Hyde substation.

A National Grid Spokesman said: “Power supplies have been restored to all customers connected to our North Hyde substation, including Heathrow, allowing operations to resume at the airport.

“We are now implementing measures to help further improve the resilience levels of our network.

“We are deeply sorry for the disruption caused and are continuing to work closely with the Government, Heathrow and the police to understand the cause of the incident.”

Ellen Deasy, 29, was surprised by her cousin Jenna with a holiday to Venice for her 30th birthday but had to settle on Portsmouth instead.

With dreams of gelato and gondoliers dashed by the Heathrow Airport fire, she told The Independent: “We woke up at about 3.30am and the first thing we saw were pictures of this fireball and the headlines.

“We were planning on riding the gondolas, eating some pasta and having some ice cream, but now we are going to Portsmouth.

“I was so excited. It would have been a dream birthday but now my thirties haven’t started in the way I hoped.”

British Airways has temporarily suspended its “empty middle seat” policy in business class on flights within the UK and between London Heathrow and Dublin.

Seats on BA short-haul aircraft are identical in business and economy. To offer premium passengers an improved service in the business-class portion of the plane, normally the middle seat in each row of three is left empty.

But in order to carry as many passengers as possible on domestic flights and the key Heathrow-Dublin route, the middle seat will now be occupied.

The move will increase capacity by around two dozen extra seats on each flight.

British Airways did the same in the aftermath of the Nats air-traffic control failure in August 2023.

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

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

He told ABC News: “Typical England — got no back-up plan for something happens like this. There’s no contingency plan.”

Heathrow is Europe’s largest airport, with more than 83.9 million passengers travelling through its terminals in 2024.

But Friday’s fire is believed to be the worst disruption at Heathrow since December 2010, when thousands of Christmas getaway passengers camped in the terminals because of widespread cancellations caused by snow.

In April of that year, air travel was grounded across Europe because of an ash cloud caused by an Icelandic volcanic eruption.

Counter-terrorism officers from the Metropolitan Police have been leading the investigation into the cause of the fire, which did not result in any casualties at the scene.

“After initial assessment, we are not treating this incident as suspicious, although inquiries do remain ongoing,” Commander Simon Messinger said.

Thousands of homes were left without power and more than 100 people were evacuated after a transformer within the substation caught fire.

Ruth Cadbury, chair of the Transport Select Committee, has been speaking exclusively to The Independent.

“Like everyone I feel most for the 200,000-old passengers who were affected – but also the airline and airport staff who have to deal with the frustration and stress of all those passengers who either need to get home or have to get to weddings, funerals, to start a holiday.

“All of those people who were due to fly yesterday and are still planning to make that journey – it could be days before they’re sorted out.”

Ms Cadbury, who is Labour MP for Brentford and Isleworth in west London, said questions about the resilience of the electricity supply in the area needed to be answered.

“We don’t actually know whether the issue is the responsibility of Heathrow airport or National Grid infrastructure,” she said.

“We have a grid capacity challenge in outer west London due to a lack of enhancements coming in, and the data centres – of which we have a cluster – taking so much power.

“Hopefully in the days or weeks to come, we will know more.”

Asked if anyone should be fired for this, Heathrow chief executive Thomas Woldbye told BBC Radio 4’s Today programme: “I’ll look back at that when I have all the details.

“Right now our focus is to make sure our passengers are safe and secure, that the airport is operating as it should so we can get aircraft in the air and get our passengers travelling.”

Asked if he should still be in his role, he said bluntly: “No comment to that. I’ll let others judge if they think that’s an issue.”