Great Britain’s grid operator warns heatwave could strain power supplies

Great Britain’s National Energy System Operator has issued a fresh electricity margin notice for Thursday evening, warning that extreme heat could tighten power supplies during the peak period.

NESO said its forecasts pointed to tight electricity margins and gave market participants the opportunity to make additional generation or flexibility available. The operator said the notice is a routine balancing tool and that there is no risk to customer electricity supplies.

Why the warning matters

The warning comes as the UK enters its third heatwave of 2026, with temperatures in southern England forecast to reach 34C and the hot spell expected to last more than 10 days.

Heat can strain the power system in two directions at once: it can lift demand as households use fans and air conditioning, while also reducing the availability of some generation.

In this case, NESO said extreme temperatures across Europe were also cutting some generation availability, adding pressure to the British grid at the evening peak.

June precedent and wider European context

This is not the first time this summer that heat has prompted a grid warning. During the June heatwave, Great Britain recorded a provisional June temperature record of 37.7C at Lingwood in Norfolk on June 27, and NESO also asked for extra electricity support.

The current warning sits within a broader European heatwave that has affected power supply conditions on the continent. Reporting on July 9 said France’s EDF expected high temperatures could reduce output at up to five nuclear plants because warmer river water can affect reactor cooling.

For Great Britain, the immediate issue is the evening peak on Thursday. NESO says the margin is tight, but it is treating the notice as a normal system-balancing step rather than a customer-supply emergency.

What to watch next

The key questions now are whether NESO extends or escalates the notice, whether generators or interconnectors are asked for additional capacity, and whether continental heat-related outages or deratings increase.

Another variable is demand: if temperatures in southern England reach forecast levels, evening electricity use could rise further and keep margins tight longer than expected.