A defect on the railway tracks was identified near the location where a train derailed in East Sussex, resulting in 30 injuries, according to an initial report.

The Rail Accident Investigation Branch (RAIB) has launched an investigation into the incident, which occurred last Thursday near Lewes. The derailment saw three carriages of a Southern Rail train tumble down an embankment. Several passengers on other trains had previously reported experiencing rough riding at the same location.

Investigators used CCTV footage from a train that passed the crash site shortly before the derailment. This footage, captured at 14:04 BST, revealed an irregularity in the track geometry just before the point where the train subsequently came off the rails. The train in question was traveling from London Victoria to Eastbourne and derailed in the Landport area of Lewes at approximately 15:54 BST.

The RAIB's continuing investigation will examine how the section of track was inspected and maintained, the condition and upkeep of the embankment, and the effectiveness of measures taken to mitigate the impact of hot weather. The derailment occurred during a period of sustained hot and dry weather, with temperatures reaching as high as 33°C (91.4°F) shortly before the crash.

Two people sustained serious injuries, while 18 others were hospitalized with less severe injuries. All 18 have since been released from hospital. The eight-carriage train was traveling at around 65 mph, which was within the 70 mph speed limit, and the driver had initiated braking as the train approached the site of the incident.

Network Rail and Greater Thameslink Railway acknowledged the incident, stating in a joint release, "We are sorry this happened on our railway." They pledged to consider all recommendations from the investigation to enhance railway safety.

Previously, Network Rail's group safety and engineering director noted that no speed restrictions were in place on that section of track at the time of the derailment. He affirmed the railway's safety, detailing measures in place to manage the effects of weather on tracks.

Department for Transport officials emphasized that safety is paramount across the UK's rail network, highlighting that delays caused by track faults have significantly decreased in recent years, positioning the UK's railways among the safest globally.