If you've been digging around for torch batteries and putting candles on your shopping list, you won't be alone. For the first time in 50 years, Britain is worrying about power cuts.

National Grid is warning that, while it remains an "unlikely" scenario, homes and businesses across England, Scotland and Wales could see their power shut-off this winter, for three hours at a time.

If energy supplies across Europe continue to be squeezed because of Russia's invasion of Ukraine, that will make blackouts more likely. But there are other factors at play too. So what should we expect?

President Putin looks set for the long-haul in his stand-off with Europe over gas supplies. So the continent will be shipping it in from elsewhere and cutting back where it can to keep the lights on.

But if there's a cold snap that pushes up demand for gas, or even worse, if there's a cold and still snap, so that the UK's wind turbines don't deliver, then we've got a problem.

In National Grid's various scenarios for the coming months, the central view remains that there will be enough energy to match previous winters.

But in a more extreme version of events, supplies of gas could worsen. That's a problem for generating electricity, because 40% of Britain's electricity comes from gas-fired power stations.

At that point distributors may be forced to cut off electricity to homes and companies for short periods. Anyone who remembers the 1970s knows what that was like.

Blackouts would be rotated, so that not all parts of the country would be affected at the same time, or on the same day.

The outages would be more likely at peak times, either in the morning when millions of people are getting up, with many corralling children and making breakfast or, more likely, the power would be off between 4pm and 7pm.

That means arriving home from school or work, not able to switch on the TV or console, not able to charge your phone or pop the kettle on, with the wi-fi down.

You can't get on with the hoovering or the washing either. And, unless you have a gas cooker, dinner is a sandwich.

Households would be able to check whether they were affected by logging on to powercut105.com and entering their postcode. But they'd also be told, at least a day ahead, of any blackouts planned, according to National Grid.

People could also receive alerts, including via text message, as they did at the height of the pandemic. And there could be Covid-style press conferences to keep the public informed of the latest measures.

But none of this can happen without the say-so of the government, and a little bizarrely, also the monarch. King Charles would receive a recommendation from the business secretary, Jacob Rees-Mogg, and would then approve the measure.

Hospitals with accident and emergency departments and major airports would be protected from the power outages.

Businesses and services can apply to their network operator to be added to the so-called Protected Sites List to avoid being cut off but it's not automatic. So the Energy Networks Association industry body recommends organisations that need protected status apply for it.

There are also calls for vulnerable households to be prioritised.

"We are thinking, for example, of older people with chronic health conditions who have to remain warm," says Caroline Abrahams, charity director at Age UK. "Or others who depend on electricity to run essential equipment, including home dialysis machines."

The Energy Networks Association says that customers who are medically dependent on electricity will be aware of what to do if there is an outage. This is because "power cuts can occur from time-to-time during a typical year, including during severe weather, for regular maintenance or due to damage and other routine faults."

It says that many people who rely on vital equipment have back-up power sources, but advises those affected to get advice from their healthcare provider.

National Grid insists power cuts are a worst-case scenario. It also has some contingency measures in place.

Coal-fired power stations are on standby in case extra generation is needed.

From next month it is also launching a scheme that offers a financial incentive to homes and businesses to reduce electricity use at key times. The scheme was trialled earlier this year, and is now being scaled up.

That strategy could help avert blackouts if there are days when supply can't match demand, by persuading some users to put off using their dishwasher or charging their electric car, until more power is available.

With measures such as this in place, National Grid thinks supply interruptions can be avoided altogether. That way the candles can be just for atmosphere.

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