Could the UK have a Spain-style blackout? What the official plans say

How likely is it here?

The government's National Risk Register 2025 says Great Britain has never had a nationwide loss of power and that the likelihood is low. It still plans for one, because a national blackout would hit almost everything else.

For this winter, the National Energy System Operator (NESO) says Britain's electricity supply is expected to stay secure. Its Winter Outlook 2026/27, published on 23 October 2026, forecasts a margin of 5.9 GW, about 9.5% above peak demand. If you hear about an "Electricity Margin Notice", NESO says it's a routine signal that more generation may be needed, not a sign that supplies are at risk.

Power cuts you're far more likely to see are local ones, from storms or faults. The government's register notes that storms Arwen and Eunice in winter 2021/22 left thousands of homes without power.

What happened in Spain and Portugal

• On 28 April 2025 at 12:33 (Spanish time), the power systems of mainland Spain and Portugal went down completely. Europe's grid operators (ENTSO-E) call it the most severe blackout on Europe's grid in over 20 years.
• Their expert panel's final report, published on 20 March 2026, found no single cause. Problems with controlling voltage led to a fast chain of power stations disconnecting, and the automatic safety systems couldn't stop it.
• Getting the power back: Spain's grid operator, Red Eléctrica, says parts of several regions had power again from about 5pm the same day. By 4am the next morning all its transmission substations were live again, and by 7am on 29 April, 99.95% of demand had been restored.

So the Iberian grid was back within about a day. Britain's own planning scenario is longer.

What the UK plans for: the first hours and days

The National Risk Register's "reasonable worst case" for a failure of Great Britain's national grid assumes it happens in winter. It doesn't give an hour-by-hour timeline, so the steps below use only what it and other official advice say.

The first minutes

• Power goes off everywhere, at once, without warning, for anyone without a back-up generator (National Risk Register).
• Gas boilers, gas ovens, heat pumps and home internet won't work without power (Be Ready).
• Report it and check for news: call 105 or check your network operator's website if you can. In a nationwide failure, expect phone lines to struggle.

The first few hours

• Phones and internet: the register says a nationwide loss of power would hit mobile and internet networks. Be Ready says your mobile may stop working if your local mast has no power. Emergency calls to 999 or 112 from a mobile can use any network that's still working.
• News comes by radio. The UK Chief Medical Officers have written scripts for broadcast during a total power outage. They say phone, internet and television would be disrupted, so public advice would come by radio. Switch on a battery or wind-up FM radio.
• The fridge: the Food Standards Agency says a fridge should stay cold for up to 4 hours. Keep the door shut.
• Small pockets of homes start getting some power back, on and off, "within a few hours" (National Risk Register).

Day 1 to day 3

• Water and sewage: the register lists water and sewage among the services hit. The Chief Medical Officers' scripts say:
• don't flush the toilet, because the sewage system wouldn't be working;
• use limited water only for drinking, handwashing and preparing food, not for showers or baths;
• share one washing-up bowl of water with soap or household disinfectant for handwashing. Our post on emergency toilets when the water is off covers the bag method.
• Food: eat chilled food first, then food with a short life, like bread and fresh fruit, then cupboard food (Chief Medical Officers, FSA). A full freezer should keep food frozen for up to 48 hours, or 24 hours if half full (FSA).
• Cooking: don't cook indoors on anything that burns fuel (see the warning below).
• Paying for things: card machines and cash machines need power and networks. Be Ready says keep some cash in case electronic payments or cash machines are down. See how much cash to keep at home.
• A large share of demand is back "within a few days", forming a stable basic network (National Risk Register).

Up to a week, and after

• Full restoration could take up to 7 days in the register's worst case.
• Some critical services could take several months to fully recover, depending on the cause and the damage.
• The register says rural areas may get power back sooner than cities, because city networks are more complex, and northern regions may be quicker because of where power stations are.

Carbon monoxide: the danger in a long power cut

The NHS lists headache, dizziness, feeling sick, tiredness and confusion among the signs. If you notice them, get outside and get medical advice.

What to have ready

These come from Be Ready's checklist and power cut page:

• Water: 3 litres per person per day, for at least 3 days.
• Food that needs no cooking, and a tin opener.
• A torch and spare batteries. Be Ready says torches are safer than candles.
• A battery or wind-up radio, with your local FM frequencies written down.
• A charged power bank for each phone.
• Some cash, in coins and notes.
• Warm layers and blankets for a winter blackout.
• Your load block letter: find it at powercut105.com or on your bill. Be Ready says it only matters in a rare national shortage, when areas might be cut off for about three hours at a time.
• If someone at home relies on powered medical equipment, sign up to the Priority Services Register and ask the equipment provider what to do without power.

What we couldn't find

• There is no official UK hour-by-hour timeline for a national blackout. The steps above follow the order of the National Risk Register's recovery description and other official advice; the timings are only those the sources give.
• We haven't included figures on how long mobile masts or radio transmitters run on back-up power in the UK. They aren't published.

Related guides

• Long blackout or cyber attack: keeping your household going
• Will there be blackouts this winter? What the 2026/27 outlook says
• Power cuts in the UK: what to do
• Power cut kit: what to keep in one box, and how long power cuts last
• Fridge and freezer in a power cut: how long is food safe?

Free tools

• Power cuts near me
• Fridge and freezer power cut timer
• Power bank and power station runtime calculator

We're an independent UK site, not the government. We check guides against official sources and link to them. In an emergency call 999.

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