As the first snow of winter falls and the mercury plummets below zero this week, Britain’s energy supply is facing its biggest test since Vladimir Putin invaded Ukraine.
“Both this week and next week will give a good indication of how safe the UK supply is and we got a taste already on Monday and Tuesday last week,” says Fabian Rønningen, analyst at Rystad Energy.
A surge in hourly energy prices in the wake of that temperature drop was “an indication of a power system under a lot of pressure and close to the limit”, he says.
The so-called “Troll from Trondheim” – a cold blast from the Arctic – is sending a chill down Britain with temperatures expected to plunge to as low as minus 8, forcing households to reach for the thermostat. National Grid only narrowly avoided enacting its blackout plan last month, and a chilly winter will present an even greater threat of blackouts.
After a mild November lulled many observers into a false sense of security, the Met Office has issued an amber “severe weather” alert over the freezing temperatures.
Experts warn that a period of cold, combined with low wind speeds and nuclear problems in France, leave the UK power system extremely stretched.
National Grid said that its “base case” is that the UK will avoid power outages, but warned that blackouts may occur in a scenario where electricity imports are reduced, combined with insufficient gas supplies.
Its boss John Pettigrew has admitted there could be rolling blackouts on “those deepest darkest evenings in January and February”.
“It's still unlikely that we would experience any temporary power cuts or still less gas shortages,” says Jeremy Nicholson, an energy market expert at Alfa Energy.
“But the risk of it is significantly higher this winter than it's been for many, many years.”
Tightening supplies will worry many households this winter, but he says it will likely be industrial users that power down if prices soar with some protection for consumers.
“It will admittedly help keep the system secure for everyone else but potentially at a terrible economic cost,” Nicholson says.
“You can safely put on the cooker for our Christmas dinner. Meanwhile, there'll be steel producers, chemical works, glass and paper manufacturers that will be curtailing their production, possibly even shutting plants altogether for a period of time.”
The UK and Europe are starting the cold snap in a better position than many imagined when the war erupted but still risk being punished for past mistakes and failing to diversify supplies.
For the UK, three major factors will be crucial this winter: temperatures here and abroad; wind speeds; and how much it can import from abroad.
While wind power can at its peak generate more than half of the UK’s power on stormy days, on calmer days it produces very little. This leaves gas to pick up the slack in terms of electricity generation, while solar power also produces less in the winter and makes up a far smaller chunk of capacity.
“As it stands now, wind power once again looks to return to relatively low levels for the year in the next couple of days, but remains higher than what we saw Monday/Tuesday last week,” says Rønningen.
“However, it is expected to get much colder and stay cold for the rest of this week, and into next week as well.”
He says that most price forecasts are “indicating that the supply situation will be very tight by the end of this week”, leading to “extreme prices returning” at some points.
Help from across the Channel may be in short supply, particularly when the whole region suffers a cold snap.
Half of France’s ageing nuclear fleet was taken offline for maintenance this year and it is still far from full capacity, even as EDF scrambles to bring reactors back online. Meanwhile, British exports of gas through the undersea pipelines to Belgium hit their highest level since at least 2016 on Sunday
French nuclear availability is now back above 60pc for the first time in many months, and five new reactors are scheduled to come online later this week as well, potentially offering some much-needed breathing space.
During a normal winter, the UK depends on imports from France to meet demand, especially during peak hours in the early evening.
If there are more delays in bringing reactors back online, it could restrict how much the UK can import at peak times.
“In the winter, we normally get energy from France," says Jess Ralston, an analyst at the Energy and Climate Intelligence Unit.
“We import it because they have the nuclear. In this coming winter, particularly in January/February, we'll start to see whether that has an impact on us. So far it hasn’t – we’ve been able to give them power.”
Some lament the UK’s own lack of action to beef up its energy security, particularly on gas storage and its nuclear capacity.
Britain still produces a chunk of its own gas and has liquified natural gas (LNG) terminals to take in imports from the likes of Qatar. But it has just a fraction of the storage available in countries such as Germany and Italy.
The Rough gas storage facility in the North Sea has been reopened, but Robert Gross, director of the UK Energy Research Centre, says it can only hold a few days or weeks’ worth of gas.
Russia choked off supplies of gas through the network of pipelines running into Europe after its invasion of Ukraine. But storage has been filled up across Europe during the summer and remained above 90pc following a mild October and November.
“Most of the rest of Europe has managed to do a very good job of refilling their gas storage over the summer so that gives us a buffer,” says Gross.
“But it does only take a fairly small number of things to be going in the wrong direction before things start to get more tight in terms of supply.”
He says a major mistake of past governments has been to push for a shift away from contracts that locked in supply and a price in the longer term.
“We really pushed for a move to a liberalised market, which is entirely dominated by spot market short term prices,” he says.
“We are now suffering the consequences for that.”
It means the UK is now competing on global markets for LNG that will go to the highest bidder, causing a scramble if cold weather hits multiple heavy users such as in Asia.
However, the UK is at an advantage to much of Europe by having LNG terminals to easily import gas from abroad – even if this comes at a huge cost.
“We do have the LNG infrastructure, which means that we could help Europe fill their gas storage and hope that they give it back to us if we need it,” says Ralston.
“But it does mean that we're more reliant on that trust than we perhaps would be if we had lots of energy storage.”