Extreme weather is an operational stress test, and in critical sectors the results are examined later, calmly and in detail. Great Britain's electricity system is now going through exactly that process for the prolonged hot spell of 22 to 26 June 2026.
On 19 October, Ofgem updated its inquiry into how the electricity system was operated during that week. It has received NESO's preliminary report, a factual account commissioned under terms of reference published in July, and set out its updated lines of enquiry: the security of the system, operational planning and decision-making, interconnector flows, demand forecasting, generation availability, balancing services and the response of the wider market. Ofgem has drawn no conclusions yet. It aims to publish its view on whether the system remained secure, and whether security standards were maintained, no later than 31 January 2027, with a timebound lessons-learned plan by 31 March 2027. Enforcement investigations remain possible if it finds material reason to believe a licensee did not comply with its obligations.
NESO's preliminary report confirms that system frequency stayed within statutory limits throughout the week; its final report is due in December. Separately, the independent Eversheds Sutherland investigation into whistleblowing allegations about operational decision-making and record-keeping in NESO's control room concluded the allegations were unsubstantiated, finding no evidence of inappropriate influence over decisions or of records being altered. It did identify areas for improvement in how colleagues raise concerns and how those concerns are acted on. NESO has accepted the recommendations in full, with board oversight of the implementation plan.
AV Resilience interpretation
The useful lesson for operators of critical services is not about electricity. It is that decisions made quickly under operational pressure will later be replayed slowly, by people with more data and no time pressure, and judged against standards, records and forecasts. Ofgem's lines of enquiry read like a checklist for any essential-service operator: planning assumptions, decision-making, dependencies on cross-border flows, forecasting accuracy and market or supplier response.
Worth testing in your own organisation:
- Could you reconstruct, months later, why a specific operational decision was taken, on what information and by whom?
- Are your forecasting and planning assumptions documented well enough to defend after the event?
- Do your escalation routes show when and how concerns changed an operational decision?
- Can colleagues raise a concern about operational practice and see it acted on, without waiting for a whistleblowing investigation?
What AV Resilience can do
AV Resilience Consulting helps operators and regulated firms prepare for exactly this kind of retrospective scrutiny. Our operational resilience design work maps important business services end to end, sets impact tolerances and builds the governance that keeps decision-making, escalation and records defensible. We also design and run scenario exercises, including severe-weather and supply-constraint scenarios, with a regulator-style after-action review, so the lessons are learned in rehearsal rather than extracted by an inquiry.
Primary sources
NESO: independent investigation concludes allegations were unsubstantiated, 19 October 2026
NESO preliminary report: Review of Electricity System Operation during Extreme Heat, 22-26 June 2026
