What happened

Storm Arwen struck Great Britain on 26–27 November 2021 with exceptionally strong northerly winds, felling trees onto overhead lines and damaging electricity-distribution networks across Scotland, northern England and Wales. The Energy Networks Association said around one million homes and businesses lost power at the storm's peak, with Northern Powergrid, SP Energy Networks and Scottish and Southern Electricity Networks all reporting large numbers of affected customers; some rural properties, particularly in Aberdeenshire and other parts of northeast Scotland, remained without electricity for over a week despite network operators mobilising additional engineers and generators. Three deaths were reported across the UK in storm-related incidents during the same period, such as falling trees, and are not all specifically attributed to the power cuts. Ofgem, the UK energy regulator, subsequently opened and, six months later, published a review into distribution network operators' preparation for and response to the storm, examining communication failures, restoration timescales and compensation payments; the review identified shortcomings without asserting that the storm damage itself was foreseeable or preventable to any specific standard. This was an accidental weather-driven infrastructure failure, not an attack, and is recorded as a major grid-reliability event given the scale of the outage and the resulting regulatory scrutiny.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.