Fears are increasing of possible winter power cuts in the UK after it emerged that National Grid was forced to issue an emergency appeal to keep the country's lights on last week.
The power network's electricity system operator (ESO) issued an emergency instruction to operators of the Nemo cable running between Belgium and the UK to make sure supplies were sent to Britain, after failing to secure enough in the normal market.
Experts told the Telegraph it cast doubt on the Grid's ability to cope during the "looming iceberg" of winter, when gas supplies are expected to be under far more severe pressure and Vladimir Putin, president of Russia, may cut off shipments to Europe altogether.
The Grid's notice, issued at lunchtime on Wednesday, came as high demand in the UK and constraints moving power into the south-east of England coincided with high demand on the continent and outages in France's nuclear fleet.
Two days of record-breaking temperatures last Monday and Tuesday also put power supplies under strain. Heat reduced the efficiency of solar panels and other generators and disrupted transmission lines, just as demand rose and wind power fell.
The strain triggered two automatic warning notices to the market last Monday calling for more generation to come online, with analysts at Cornwall Insight warning that demand came "very close" to outstripping supply.
The ESO said automatic market signals did not take into account all of its data and tools, and it was confident that electricity margins were sufficient.
Early forecast from ESO
It comes as the ESO is this week set to publish its early forecast for power supply and demand this winter, amid heightened concern over energy security owing to Russia's war on Ukraine.
While the heat created particular challenges last week, demand for energy is typically higher during winter. Cold snaps in particular can cause havoc with infrastructure.
Kathryn Porter, an energy consultant at Watt-Logic, told the Telegraph: "The warnings from National Grid during hot, still weather are a sign of worse to come in winter when cold, still weather will stress the system even further."
Britain gets most of its electricity from its own gas-fired power stations, nuclear plants, wind turbines, biomass and solar plants.
It also trades power with the Continent through a growing web of cables capable of supplying more than 10% of UK demand.
Meanwhile, it has emerged that British households could be asked to turn down their thermostats and switch off their lights under Government plans to avoid winter blackouts.
Emergency contingency plans for a gas or electricity supply shortage include public appeals to use less energy.