The National Energy System Operator (NESO) has issued its third electricity margin notice (EMN) of 2026 as the UK experiences its third heatwave of the year, with temperatures peaking at 35°C in parts of the country. The warning, which calls for additional electricity supply, comes amid heightened demand for power to run cooling systems and fans.
Record-Breaking Temperatures and Energy Strain
The Met Office confirmed a heatwave warning earlier this week, with temperatures soaring well above average across much of the UK. Dr Amy Doherty, Met Office Science Manager, noted: “This year has already seen a number of remarkable temperature milestones. Not only have we now recorded a record eight days with temperatures exceeding 34°C, surpassing the previous record held by 1976 and 2020, but it is also the first year in the UK weather record to see temperatures reach 35°C or higher in May, June and July. These records highlight just how notable this year has been for UK temperatures, with exceptional warmth observed across multiple months.”
The NESO warnings, typically issued during cold snaps, have now been deployed three times between June and July 2026 – a first for the operator. The last EMN before June was in January 2025, and prior to that, March 2023. While the notice does not indicate an imminent risk of blackouts, it signals that NESO is managing a tighter margin between electricity supply and demand.
Impact of French Nuclear Power Outages
High temperatures in France, a key source of electricity imports for the UK, have forced some French nuclear reactors to power down due to insufficient cooling water. This has reduced the amount of electricity available for import, adding pressure on the UK grid during peak demand.
NESO had previously outlined plans to address energy supply surpluses, as demand is typically higher in winter. However, the repeated summer warnings indicate unusual strain on the system, exacerbated by global factors such as the war in Iran and depleted European gas storage facilities, which have driven up energy costs worldwide.
Health Alerts and Public Advice
Amber and yellow heat health alerts issued by the UK Health Security Agency (UKHSA) remain in place across large parts of England until July 12, with temperatures expected to stay well above average. Britons have been advised to unplug certain appliances that generate additional heat in homes to reduce both indoor temperatures and electricity consumption.
NESO’s repeated warnings underscore the challenges of maintaining grid stability during extreme weather events, which are becoming more frequent due to climate change. The operator continues to monitor the situation closely and may issue further notices if demand outstrips supply.
