Harry Farley
Political correspondent

Image source, Reuters

The prime minister’s spokesman says “there are questions to answer” over how a fire knocked out Heathrow.

No 10 says “we expect those questions to be answered” but the priority is bringing the fire under control, adding it was too early to speculate on whether foul play was involved.

Downing Street could not say if it was confident the airport would reopen at midnight as planned, adding the prime minister is being kept updated.

“It’s clearly a fast-moving situation,” the spokesman says, adding it “wouldn’t be unreasonable to expect checks on resilience” are being carried out at other major airports.

The Cabinet Office is leading the government response. A multi-agency call was held earlier involving officials from the transport department, the energy department, National Grid, the Civil Aviation Authority, the National Air Traffic Services, and emergency services.

Image source, BBC News

While some Heathrow-bound flights have been diverted, others have had to turn back mid-flight.

Adam Brown is back in Washington DC after his flight got halfway across the Atlantic before making a U-turn.

He tells the BBC there wasn’t much support after landing – it was a fend-for-yourself situation, he says.

Image source, Getty Images

Here's what you need to know this lunchtime:

• Heathrow Airport, one of the world's busiest, is closed all day after a fire broke out at an electrical substation in Hayes, west London, last night
• Nearby residents were evacuated. One told the BBC: "Suddenly there was this huge bang and the house just shook"
• Counter-terrorism police are leading the investigation, but the Met Police says there's "currently no indication of foul play"
• In an update at 11:00 GMT, London Fire Brigade said the fire was still burning and power remained out in Terminals 2 and 4
• Heathrow has warned of days of disruption, with more than 1,350 flights affected today. Nearby pubs and hotels are crowded with stranded passengers
• Some flights have been diverted to cities including Glasgow, Amsterdam, Frankfurt, New York JFK and Paris

We've also outlined in a post what to do if your flight has been cancelled.

Stick with us as we bring you the latest.

Tom Espiner
Business reporter

Image source, PA Media

A source at Heathrow says the airport has back-up systems to deal with situations like an aircraft in distress, but not for the entire airport.

Heathrow has interconnected systems, including IT, heating and lighting. Some have back-ups, but others are still offline, the source says.

Jonathan Josephs
Business reporter

Image source, Reuters

Delta Air Lines says it's cancelled 10 flights from London Heathrow today.

Four planes were already on their way when they were alerted to the closure. One returned to Minneapolis–Saint Paul, while three were diverted to Amsterdam. Passengers on those flights have been offered a Eurostar train to London or a connection to their final destination.

Meanwhile, United Airlines has cancelled all 17 flights it normally operates from Heathrow each day.

It says seven flights had to return to their origin or divert to other airports. Passengers are being offered alternative options to reach their destinations.

Simon Jack
Business editor

Image source, PA Media

A National Grid source tells the BBC that power should be back on "in hours" at Heathrow airport, but it's too soon to say exactly when.

As we just reported, the airport has multiple sources of power. National Grid says the Hayes substation "was a particularly important bit".

National Grid source says the organisation accepts that there were important questions to ask around resilience, but their current efforts were being directed to restoring power as soon as possible.

Mark Broad
Business editor

A Heathrow source tells the BBC that they have "multiple sources" of energy at the airport - with diesel generators and "uninterruptable power supplies" in place.

The source says that when the power outage happened the back up systems "all operated as expected".

The systems, however, are not enough to run the whole airport – hence the decision to close it down.

The source says the airport is in the process of redirecting power to the affected parts of the operation – but that it "takes time".

Image source, EPA

Transport Secretary Heidi Alexander says she’s spoken to Heathrow Airport’s chief executive and is "reassured they’re working tirelessly to reopen" as soon as possible.

She thanks emergency services for their response and urges passengers not to travel until told otherwise.

We've also heard from London Mayor Sadiq Khan, who says electricity suppliers are working hard to restore power in the area.

"I know this will be hugely frustrating for the many thousands expecting to travel to and from Heathrow today, the families who have had their power cut and the commuters who have had their journeys disrupted," he says.

Your Voice, Your BBC News

Some of you have been asking if counter-terrorism police investigating the fire means it was an act of sabotage.

BBC home affairs correspondent Daniel Sandford says the fire has caused "extraordinary damage" to a key part of the UK's national infrastructure, which is "something that a hostile state or a terrorist group would like to cause".

"We need to be asking the question: has that been caused by a hostile state or a terrorist group?" he says, adding that there is "no evidence at this stage that that is the case".

Counter-terrorism police will be checking if any device or initiator started the fire, as they specialise in investigating explosions and fires, Daniel Sandford says.

"There is no suggestion at the moment of sabotage or foul play, but everybody agrees they need to be asking the question just in case," he says.

We're answering your questions on the Heathrow shutdown as part of our Your Voice, Your BBC News project.

Audience member Paul asks how there can be a single point of failure to the electricity supply to Heathrow Airport, which is such a key part of the UK's infrastructure.

A Heathrow source has told the BBC the airport does have back-up systems to cope, for example, with an aircraft in distress, but it doesn't have a back-up system for the whole airport.

BBC home affairs correspondent Daniel Sandford says the possibility of alternative, comprehensive back-up power supply will be a key question once the dust has settled.

He also poses the question as to whether other parts of the UK's national infrastructure have the same issue.

Paul Ward
Journalist, BBC Scotland

A flight from New Orleans heading to Heathrow was diverted and touched down at Glasgow around 10:30 GMT. Passengers said they were told about an hour before landing that it had to divert.

For some, there was a scramble to rearrange travel.

Vanessa Connell and partner Simon spent almost £1,000 on flights from Glasgow to Gatwick.

She says: “We have a wedding tomorrow so we have to get back. We’ll hold on to the receipts.”

For others, the diversion made their onward journey easier.

Allan Strachan lives in Edinburgh so was pleased to be landing in Glasgow.

“It’s good for me but I feel sorry for all the people that have to rush to sort things out," he says.

Wesley Stephenson
BBC News data journalist

The closure of Heathrow Airport has impacted travel across the globe, with many flights due to land in London being diverted to other airports.

As you can see in this chart based on FlightRadar data, Amsterdam tops the list with seven flights diverted to its airport. That's followed by Frankfurt, Washington, London Gatwick, Shannon and Paris with six flights diverted to each airport. New York's JFK, Madrid, Manchester and Glasgow have each taken in five diverted flights.

Rich Preston
Reporting from Heathrow

Image source, Reuters

The ripple effects of today’s closure of Heathrow airport will be felt far and wide - and for several days to come.

Hotels and pubs around the airport have crowds of people sitting in their lobbies and at tables, surrounded by their luggage and looking despondently at their phones, desperate for any kind of good news.

I’ve spoken to groups who were supposed to be going on holiday, to weddings, to business meetings.

Some are trying to get home to see family, or are on the last leg of a big trip. Heathrow was the airport with the most international connections in the world in 2024, according to industry travel data provider OAG, so many of these people won’t have even been visiting the UK but are merely passing through as they travel between Asia, Europe, and America.

But as well as people passengers, it’s important to remember cargo.

Heathrow is a major cargo hub - last year it served 234 destinations handling more than £190bn worth of goods. In 2023, 48% of all UK air cargo travelled through Heathrow, according to the airport itself - handling everything from medicines, fresh fruit and veg, books, tech items, fresh flowers - and even live animals.

Even when the airport does get its power back, it will take days before any semblance of normality is resumed with a huge backlog of both goods and people waiting their turn to get through Heathrow.

Heathrow Airport is going to be closed all day because of a fire at an electricity substation which caused a power cut - and travellers are being warned there'll be significant disruption over the next few days.

Here's what you need to know:

As we continue to update you with the latest developments on Heathrow Airport's closure due to a nearby substation fire, we've lined up several experts to answer your questions on what has been called an "unprecedented event".

You can follow along from 12:30 by pressing Watch live at the top of the page.

As a reminder, you can get in touch with us via Your Voice, Your BBC News.

Daniel Sandford
Home Affairs correspondent

The impact of the electricity substation fire near Heathrow has had a devastating impact on a key part of our national infrastructure - the kind of impact that terrorist groups and hostile states would like to have.

At the moment it looks like a fault, but what if it was deliberately started? That question needs to be ruled out urgently.

That is why counter-terrorism detectives are leading the investigation into the cause of the fire. They have specialist forensic skills and can look for any evidence of an explosion or other deliberate act.

Also if at any stage foul play is suspected counter-terrorism detectives will want to have been involved from the start.

If foul play remains ruled out, there is another urgent question: How many other key parts of our national infrastructure do not have a backup electricity supply?

Jonathan Josephs
BBC business reporter

The International Air Transport Association (Iata), says today’s closure of London Heathrow is "yet another case of Heathrow letting down both travellers and airlines".

The director general of the airline trade body Willie Walsh - a former pilot and CEO of British Airway’s parent company IAG - says "it begs some serious questions" about how an internationally important piece of infrastructure can be totally dependent on a single power source.

In a statement he also suggests it is unfair that his members, which are 340 airlines that account for over 80% of global air traffic, will have to pick up the bill for taking care of passengers for an event that is not their fault.

He says that without finding a "fairer allocation of passenger care costs", Heathrow has "very little incentive to improve".

Marta Newman
BBC News at One producer

Image source, EPA

As passengers wonder about their rights in regards to cancelled flights, I've just spoken to Graeme Buck, the Director of Communications at travel trade association ABTA.

He says that if a passenger's flight is cancelled they must be offered the choice of a replacement journey, or a refund.

"That flight should be as soon as possible," he explains. "If you find you have to stay overnight somewhere or you incur extra costs travelling to different airports to get back to Heathrow then you should be compensated for that as well."

If you've booked a package holiday, you may also have additional rights under the package holiday travel regulations, he adds.

Tom Edwards
BBC London Transport Correspondent, reporting from Heathrow airport

Image source, Getty Images

A line of trolleys blocks anyone from getting into the terminals at Heathrow Airport, while there are lots of staff around and a handful of passengers looking at their phones wondering what to do.

I'm inside Heathrow airport, not far from Terminal 3, and it's absolutely deserted as the terminals are locked down.

One couple I met was due to fly to Vietnam and they have had to head home. Another was furious at the lack of information.

This will be an absolute calamity for a lot of passengers and there are bound to be questions about the airport's resilience, and how a fire at a substation can effectively knock out one of the world's busiest airports.

Sources from within aviation have expressed their anger at what has happened. They want to know why there was no back up.

They say Heathrow is an international “laughing stock” and the lack of preparedness is “shocking”.

There is no indication the fire was caused by foul play, the Met Police says in a statement, but adds it is keeping an open mind at this time.

A spokesperson for the force says: “We are working with the London Fire Brigade to establish the cause of the fire which remains under investigation. While there is currently no indication of foul play we retain an open mind at this time.

“Given the location of the substation and the impact this incident has had on critical national infrastructure, the Met’s Counter Terrorism Command is now leading enquiries.

“This is due to the specialist resources and capabilities within that command that can assist in progressing this investigation at pace to minimise disruption and identify the cause."