But during Wednesday evening’s peak, the data show that wind’s output was just 2.5GW. At that time, the total consumed across the UK was almost 19 times as much at 46.825GW.

And this, it should be remembered, is now, when Britain still has a large fleet of gas-fired power plants it can rely on. However, Miliband and Neso have pledged that by 2030, Britain will be a “clean energy superpower” having almost eliminated fossil fuels from its grid. Even if this goal is not met, it is certain to be far more dependent on “weather based” renewables.

The cliff edge over which we almost tipped was not unforeseen. Aware of the weather, specialist electricity market forecasters had been predicting a pinch for some time, and on Tuesday and Wednesday Neso issued a series of Electricity Margin Notices (EMNs), warning that the gap between supply and demand was going to be tight.

The reality shown by Porter’s analysis is less reassuring. EMNs, she points out, are only issued when Neso control room staff fear the margin of available extra generating capacity will not be big enough to keep the power flowing in the event of a serious fault developing somewhere in the system.

They were right to be worried, for according to Porter, at 5.30pm on Wednesday, when demand was running at 46.825GW, the total available supply from all UK sources and the undersea “interconnectors” that can supply Britain with electricity generated in Europe was just 47.405GW, leaving a spare margin of just 580 megawatts (MW). Yet this was despite the fact that reserve gas plants were being fired up at enormous cost – two were paid a total of £12 million for supplying power for just three hours.

This, says Porter, was far too close for comfort: “Even a relatively small power station trip would have caused an actual shortage and triggered blackouts.” One of the interconnectors, Viking, which links Britain to the grid in Denmark, had been due to be closed on Wednesday for maintenance. It has a capacity of 700MW. Fortunately, it turned out to be available. If there had been a sudden, unexpected trip, or had Viking been offline, Neso would have been forced to impose “demand control”, meaning power cuts.

Even more concerning is the fact that, unreported until now, in the course of Wednesday — not, thankfully, during the period of peak demand — two big gas-fired power plants, Langage and Peterhead, did trip out. Their combined output is 2GW, and had they gone off at 5.30, blackouts would have been a certainty.

Had power cuts been needed, they might have been limited in scope. But in the event of a “prolonged shortfall” — not unimaginable when the government is committed to building a net zero, renewables-dependent grid — Neso says there would be “rota disconnections” affecting every region in turn to ensure “fair distribution” of the pain these would cause.

Porter says that if there had been a sudden blackout at 5.30pm, it is likely that people would have died. Traffic lights and street lamps would have ceased to function, and the only lighting from shop windows would have come from candles or lamps powered by batteries. Without electricity for their thermostats and pumps, gas-fuelled central heating systems would also have stopped working, just as the night’s frost began to bite.

Most worryingly of all, Neso did not expect this crisis until shortly before it happened. Its Winter Outlook, published in October, claimed the system’s spare capacity would be bigger than it was last year, largely because it underestimated peak winter demand by 2.4GW, which Porter describes as a “huge error”. It also overestimated how much power could be supplied through the interconnectors.

The UK power market, she concludes, came “close to disaster” on Wednesday. Neso told me the following day it disputed her findings, claiming it had merely “used our standard operational tools to manage the electricity network and ensure that we maintained enough electricity,” and that its margin had at all times been greater than 580MW. However, in the course of a dialogue that lasted for the following 24 hours, I asked its spokesperson to tell me why he thought her analysis was wrong, and what would have been the source of the additional electricity. He simply refused to answer, saying: “As an operator for the whole of Britain, we don’t talk about individual units, because we have lots of customers and technologies and we don’t set out a list of assets that could cover a particular loss.”

Either way, we may not always be lucky. Meanwhile, Centrica, which owns half of Britain’s gas storage, reported on Friday that reserve stocks are 26% lower than in January 2024, and if needed would last less than a week. The rest of the winter could be long and difficult.

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David Rose is UnHerd‘s Investigations Editor.

DavidRoseUK

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