The Rail Accident Investigation Branch (RAIB) reported on 19 August 2026 that train 1F34, the 14:24 London Victoria to Eastbourne Southern service, derailed at about 15:54 on Thursday 13 August 2026 around one mile (1.6 kilometres) north of Lewes station in East Sussex. Of the eight vehicles, the rear three derailed and overturned onto the embankment; the front five did not derail. About 150 people were on board. Thirty were injured, 20 required hospital treatment, some seriously, and the train and infrastructure were significantly damaged.

Preliminary on-train data recorder analysis indicated the train was travelling at around 65 mph (105 km/h) approaching the point of derailment, where the maximum permissible speed is 70 mph (113 km/h), on the Down Lewes line. CCTV showed a track geometry irregularity on the immediate approach, and rail marks were consistent with wheels climbing over the rails, RAIB said. The nearest weather station recorded about 27 degrees Celsius at the time, during sustained hot, dry weather.

RAIB said its investigation would examine the derailment sequence, track and embankment condition and maintenance, hot-weather mitigation, vehicle condition and crashworthiness, and the emergency response. It said findings may be refined and would be published at the conclusion of the investigation.