Britain's electricity grid came close to experiencing blackouts on June 23 of last year during a significant heatwave, according to whistleblower allegations. Shadow energy secretary Claire Coutinho informed Parliament that grid operators claimed the system failed to meet necessary security standards as temperatures climbed to 34 degrees Celsius (93.2 degrees Fahrenheit).
Coutinho further alleged that the National Energy System Operator's (Neso) corporate affairs team attempted to cover up the situation, prioritizing the organization's reputation over energy supply security. She stated that operational decisions were being recorded without an audit trail, claims the minister did not deny.
In the period leading up to the June incident, Neso issued an emergency margin call, a request for generators to increase power output, due to a forecasted shortfall. Government departments were reportedly warned about the potential for power cuts.
Energy minister Michael Shanks countered that electricity supplies were maintained throughout the heatwave and no customers experienced power outages. He asserted that statutory frequency limits were upheld and that the largest credible loss of power generation was covered. Shanks stated that the country never came close to breaching the margin, the buffer between peak demand and supply, and that no emergency situation occurred.
Despite these assurances, Shanks confirmed that Neso has initiated an independent investigation into the whistleblower claims, with a legal firm appointed to conduct the review. The findings are expected to be delivered to Neso and the regulator Ofgem in the coming weeks. However, Coutinho dismissed the investigation as a "sham," citing concerns that workers would not be guaranteed anonymity. Julian Lewis, a Conservative MP, also questioned the independence of the review, noting that Neso is funding the investigation.
Bill Esterson, chair of the Labour energy committee, shared that a Neso director found it implausible that corporate staff influenced control room decisions. Neso has issued three electricity margin notices this year, with the June event being the first such notice issued during the summer months. The operator has issued only two other notices, both in January of the previous year, since it assumed responsibility in October 2024.
Extreme heat places considerable pressure on electricity systems by reducing the efficiency of power generation, including nuclear and gas-fired plants, as well as water-cooling systems. Britain's last major blackout occurred in 2019 when simultaneous failures at a gas-fired power station and a windfarm led to automatic grid shutdowns across large areas.