What Is ‘Black Sky’ and Why Is the UK Preparing for Days Without Power?

Your phone can have a full battery and still be useless in a blackout. The tower it needs to reach might have run out of backup power. The same outage can stop the pump that gets water to your tap and the card terminal that lets you buy a bottle.

On November 7, the BBC reported how it would keep broadcasting if a prolonged power failure hit Britain. Its fallback is FM radio from an emergency studio, with generators to keep the transmitters on. The report comes after the UK government launched its Be Ready campaign on October 22, asking people to keep three days’ worth of essentials at home. An official exercise had already shown how quickly a grid failure could become a food and water emergency.

What is a ‘Black Sky’ event?

It’s a prolonged, wide-area power outage severe enough to disrupt other essential services. A storm can flood substations or bring down transmission lines. A grid fault can cascade as equipment shuts itself off for protection and the surviving network can no longer carry the load. The scale matters because the next town may be in the same position. Its shops, fuel pumps and repair crews are suddenly under pressure too.

What goes first after the lights?

In December 2015, floodwater knocked out a substation in Lancaster, England, cutting power to about 61,000 properties. Card payments failed and cash machines became inaccessible. Petrol stations shut because their pumps needed electricity. Some care homes lost heating and hot water. Mobile and internet connections failed widely. Local station The Bay moved upstairs from its flooded studio and kept broadcasting on a generator, with one phone line connecting it to the outside world.

Why is the BBC betting on FM?

A battery-powered FM radio can pick up a broadcast without a mobile signal or a home internet connection. The transmitter still needs power. The BBC says its emergency setup would use generator-backed transmitters and communications that can operate independently of the internet, with supplies to keep the operation going for at least three days. That gives authorities a way to tell people where to get drinking water even if the message can’t reach their phones.

Can Britain get the power back in three days?

Three days is the household guidance. The National Energy System Operator, which runs Great Britain’s electricity system, has until December 31, 2026, to have the capability in place to restore 60 per cent of demand in each region within 24 hours and 100 per cent across Great Britain within five days. Those are targets for restoration capability. The time a particular home spends in the dark depends on what failed and what can be reconnected.

The government ran a national outage exercise called Mighty Oak in 2023. A September 2026 audit found that many of the response plans tested were inadequate to keep essential services, including food and water, going. It also found that the department responsible for food supply had yet to meaningfully test changes it had made in response.

How do you start a power station with no power?

With a plant that can start on its own. Even power stations need electricity to run equipment such as pumps and controls before they can supply the grid. A plant equipped for a “black start” can use an independent source of power, such as a diesel generator, to get its own machinery going. Some hydroelectric stations can do this.

Operators use that first supply to bring a stretch of the network back to life and help start other plants. They reconnect demand in blocks so that generators aren’t overwhelmed. Small working sections, known as islands, can then be joined once their electrical systems are running in step. Where a neighbouring grid is still running, operators can also draw power across a working link.

Has anyone had to do this for real?

Yes. On April 28, 2025, continental Spain and Portugal suffered a total blackout. Some Spanish hydro plants started without grid power, and links to Morocco and France helped bring electricity back into Spain. Portugal’s two black-start plants got going after unsuccessful earlier attempts. Operators completed restoration of the transmission grid in Portugal shortly after midnight and in Spain around 4 am. That milestone concerns the high-voltage network. A local fault can still leave a building without power. A European expert panel later traced the collapse to several interacting factors, including voltage-control problems and generators disconnecting in succession.

What do other countries practise?

In November 2025, North American utilities and government partners rehearsed their response to simulated cyber and physical attacks on the grid in an exercise called GridEx. The organisers’ March 2026 report called for more testing of backup communications, including radio. Sweden’s civil preparedness advice goes straight to households. It asks them to be able to manage for at least a week and identifies the public broadcaster’s P4 radio network as the official emergency information channel.

Does India have a restart plan?

Yes. In July 2012, the northern grid failed one day and the northern, eastern and north-eastern grids collapsed the next, apart from a few areas. The second failure hit at 1 pm, while Delhi Metro trains were running, and brought services to a sudden stop. Today, India’s electricity grid code requires state and regional control centres to update restoration procedures each year. It requires annual drills that include black starts and tells operators to identify which essential services should get power first.

How would India get a warning out if the towers went down?

India launched a nationwide cell-broadcast alert system in May 2026. It can send a warning to compatible phones in a targeted area without relying on an app. It still needs a functioning mobile signal. India’s disaster management authority also lists radio and public sirens among the ways warnings can reach people. The practical test is local. Can a city tell residents where to get drinking water when the tower serving their neighbourhood has gone quiet?