A backstop system designed to prevent blackouts was mobilised for the first time in two years as Britain’s power grid battles low winds and nuclear outages.

The surprise notice for the capacity market, which issues a warning to Britain’s electricity generators, was issued by the National Energy System Operator (Neso) just after midday on Monday.

It told generators to be ready for when demand spikes at 4:30pm, amid fears the amount of spare power capacity had grown unacceptably small compared to demand.

However, the notice was withdrawn just after 2pm.

A spokesman for the Neso insisted it was “confident that electricity margins are sufficient for this evening” and stressed the triggering of the original notice was automatic.

The warning was the first of its kind since November 2022, when a similar notice was also issued and withdrawn as low wind speeds and nuclear power outages piled stress on the electricity system.

Moments after the notice was issued, the Neso insisted it was “confident that electricity margins are sufficient for this evening” and stressed the notice was automatic.

The warning was the first of its kind since November 2022, when a similar notice was issued but later withdrawn as low wind speeds and nuclear power outages piled stress on the electricity system.

Kathryn Porter, an independent energy analyst at Watt Logic, said the likely causes this time around were lower-than-expected wind output, as well as greater-than-expected demand for electricity.

At the same time, publicly available data showedthe grid was expecting power to be flowing out to Europe via interconnectors on Monday evening, suggesting the Neso might have had to intervene to ensure power flows into the UK instead, she added. 

The warning also comes after the Sizewell B nuclear power station, in Suffolk, was temporarily shut down for refuelling on Friday.

The 1.2 gigawatt site is not expected to return to full capacity until December, according to owner EDF.