On 19 October, Great Britain’s energy regulator Ofgem published an update on its inquiry into electricity system operations during the hot spell of 22–26 June 2026. A factual preliminary report prepared by system operator NESO says high demand, reduced generation availability and variable cross-border flows combined to create tight operating margins. Ofgem stressed that it has not yet concluded whether the system was secure or whether operating rules were followed.

The preliminary report says electricity supply to consumers was maintained and frequency did not leave the statutory 49.5–50.5 hertz limits. It also records extended periods below the normal 49.8–50.2 hertz range, especially on the evening of 23 June, and reported exceedances of internal limits on parts of the transmission network. Ofgem is investigating the significance of these events and compliance with security standards. The NESO review team is due to provide its final report in December, after which Ofgem says it will publish its independent conclusions.