Power cuts in Great Britain: how often the lights go out, and for how long

The two numbers Ofgem regulates

35.1 minutes a year without power, on average

Ofgem sets every distribution network two reliability targets. Customer Interruptions (CI) is the average number of supply interruptions per 100 customers in a year. Customer Minutes Lost (CML) is the average number of minutes each customer is without supply in a year, averaged across every customer, including the majority who had no cut at all. Both cover planned and unplanned interruptions of three minutes or longer, and both are adjusted for severe weather events before Ofgem's final assessment. In 2024/25 the sector figure for CML was 35.1 minutes, down from 36.7 in 2023/24, and CI was 39.7 per 100 customers, down from 42.5. Ofgem's own reading is that performance improved on the first year of the price control but that several companies still missed deliberately demanding targets.

Customer Interruptions (CI)

The average number of supply interruptions per 100 customers. Ofgem's definition, annual report 2024-25.

Customer Minutes Lost (CML)

The average duration of interruptions experienced by customers, in minutes per customer per year. Ofgem's definition, annual report 2024-25.

Minutes lost by licence area

SSEN Scottish Hydro customers lost 6.6 times as many minutes as UKPN London customers

Great Britain is served by 14 electricity distribution licence areas run by six groups. The bars are Customer Minutes Lost in 2024/25. SSEN Scottish Hydro, serving north of Scotland, recorded 68.9 minutes per customer against a target of 52.9. UKPN London, serving London, recorded 10.5. Rural areas with long overhead lines exposed to weather sit at the top; dense urban networks with underground cables sit at the bottom. Red marks an area Ofgem rated red against its target for the year.

Customer Minutes Lost, planned and unplanned, 2024/25, with Ofgem's RAG rating against the area's target. Customer numbers are 2025. Source: Ofgem supplementary data file, Chapter 2 reliability outputs.

Interruptions by licence area

SSEN Scottish Hydro customers were interrupted most often

Customer Interruptions counts how often supply is lost rather than for how long. In 2024/25 the range ran from 59.1 interruptions per 100 customers in SSEN Scottish Hydro to 11.2 in UKPN London. 4 of the 14 areas were above their CI target and 10 improved on 2023/24.

Customer Interruptions per 100 customers, planned and unplanned, 2024/25. Source: Ofgem supplementary data file.

Rewards and penalties

£50.9m in net penalties over the first two years of the price control

Under the Interruptions Incentive Scheme a company that beats its targets earns a reward on its allowed revenue and one that misses them pays a penalty, capped at 150 basis points of return on regulatory equity. In 2024/25 4 of the 14 areas earned a reward and 10 paid a penalty. By group, SP Energy Networks earned £2.1m and Northern Powergrid paid £9.0m. Over 2023/24 and 2024/25 together the net position across all six groups is a penalty of £50.9m, the figure Ofgem's report describes as cumulative penalties to date. Penalties are a transfer back to customers through allowed revenue, not a fine paid to the Treasury.

Interruptions Incentive Scheme total reward or penalty, £m, by group, 2024/25 and cumulative 2023/24 to 2024/25. Reconciled to Table 6 of Ofgem's annual report. Source: Ofgem supplementary data file.

Direction of travel

8 of 14 areas cut minutes lost on the year

Between 2023/24 and 2024/25 the sector figure for minutes lost fell from 36.7 to 35.1 and interruptions per 100 customers fell from 42.5 to 39.7. 8 areas improved on duration and 10 on frequency. The longer record is Ofgem's: its RIIO-ED1 performance summary for 2021-22 reported that over the previous price control, from 2015-16, customer interruptions had fallen by 23 per cent and the duration of interruptions by 18 per cent, and that every licence area met its targets that year. The targets were then tightened for RIIO-ED2, which is why an industry that is more reliable than a decade ago is now paying penalties.

Change in Customer Minutes Lost, 2023/24 to 2024/25. Green improved, red worsened. Source: Ofgem supplementary data file.

“Over RIIO-ED1 to date, customer interruptions have fallen by 23% whilst the duration of interruptions has reduced by 18%.”

The national picture

The grid has a margin this winter. The Government still says prepare for days without power

Local cuts are about wires and weather. A national shortage is a different risk, and the National Energy System Operator publishes its expectation every autumn. Its Winter Outlook for 2025/26, published 9 October 2025, forecast an operational margin of 6.1 GW, the highest since 2019/20 and about 10 per cent of average peak demand, while cautioning that some tighter periods might still occur. For the coming winter NESO's early view, published 23 June 2026, expects a surplus of 5.5 GW between 31 October 2026 and 31 March 2027, an 8.8 per cent buffer over expected peak demand, with January the month it names as most likely to be finely balanced. The full outlook is due in October and this page will be refreshed when it lands. Alongside that, the Cabinet Office's Prepare campaign says most power cuts are short and local but that longer outages could last several days with regional or, although unlikely, national impacts, and tells households to keep a battery or wind up torch and radio, bottled water and food that needs no cooking, to know the 105 number for reporting a cut, and to find their load block letter, the rota under which areas would be disconnected for around three hours at a time in a national shortage.

Questions this raises

What the figures do not settle