Late last night NESO issued an Electricity Margin Notice for 16:00–19:00 this evening, Monday 28 September. The notice gives a 1,400 MW shortfall against a 700 MW contingency requirement. It also says 1,900 MW of generation is "excluded from the available system margin due to system constraints", which is the largest exclusion of any EMN on record.
An EMN is a request for more capacity: NESO is asking generators, suppliers and interconnectors to offer more MW. It is not a blackout warning, and nearly all of them get withdrawn.
How often this happens
EMNs used to be rare. Winter 2020/21 had six, the first since 2016. Another came in January 2023. BMRS then shows none at all from May 2023 to the end of 2024, and a single one on 8 January 2025.
This summer changed that. Tonight's is the fifth EMN of 2026, and four of the five have come since late June: 24 June, 26 June, 9 July, 12 August, and now 28 September. Every earlier one was cancelled, and none escalated. On three of those evenings the cancellation came only after the window had begun or was about to.
EMNs, it turns out, are like buses: you wait 18 months for one, then four turn up in a single summer. The Prime Minister would know the feeling. As Mayor of Greater Manchester, Andy Burnham took the city-region's buses back under public control, and he'd probably say the answer to both is better coordination. One of the power stations stuck behind tonight's bottleneck, Carrington, is in the city-region he used to run.
These summer notices are also unusual in timing. EMNs have traditionally been a winter-peak event. All of 2026's cover a summer or early-autumn evening, when solar is fading and demand has yet to drop.
Tonight's notice differs from the earlier ones in several ways.