Britain's National Energy System Operator (NESO) issued an Electricity Margin Notice (EMN) on 9 July 2026, asking power stations, interconnector operators and other market participants to identify any additional capacity they could make available during the evening peak period. The notice was in effect between 6.30pm and 10.30pm, with NESO forecasting a projected system shortfall of 1,000MW. The operator cited extreme temperatures across Europe as reducing the availability of some generation while simultaneously boosting cooling demand across the UK.

NESO stressed that the notice does not signal that blackouts are imminent or that there is insufficient generation to meet demand. The alert is only the third time in the electricity system operator's history that it has warned of tight supplies during the summer months [Source: Sky News]. It is also the third EMN NESO has issued in 2026; two earlier notices sent in June were both cancelled ahead of time.

Extreme heat reduces the efficiency of multiple generation technologies, including nuclear power plants, gas stations and water cooling systems. During a previous European heat wave, several French nuclear plants went offline as they were unable to cool sufficiently. Electricity Margin Notices are more typically associated with cold winter spells, when heating demand places the greatest stress on the grid.

The grid strain comes against a backdrop of rising energy costs for consumers. The Ofgem energy price cap increased by 13% for the period covering 1 July to 30 September 2026, driven by higher wholesale gas prices linked to the ongoing conflict in the Middle East [Source: Ofgem]. Under the July 2026 cap, the average price of electricity rises to 26.1p/kWh and gas to 7.3p/kWh, leaving typical bills 53% above their winter 2021/22 level.

On the supply side, UK gas demand was forecast to jump from 78 mcm/d to 97 mcm/d mid-week as warm weather drove cooling load, with low wind across northwest Europe pushing gas-for-power generation up 14 mcm/d to 49 mcm/d in the UK. Europe's third major heat wave of the year was set to intensify and expand, extending from west to east over the coming week.

Sources: The Guardian, Sky News, LBC, Energy Live News, Bloomberg, Smart Energy UK, Ofgem, House of Commons Library, Semafor