The Rail Accident Investigation Branch has released an update into its ongoing investigation into the train derailment at Lewes in East Sussex.

At around 15:54 on the 13th August 2026, 1F34, the 14:24 Southern service from London Victoria to Eastbourne, derailed around 1 mile north of Lewes station.

The service was formed of eight carriages, and the rear three vehicles derailed and overturned, coming to rest on their side on an embankment.

150 people were on the train when the derailment happened. 30 people were injured in the accident; 20 of those required hospital treatment, some with serious injuries.

The first RAIB inspectors arrived on site at 19:11 to secure evidence alongside the British Transport Police.

The RAIB has downloaded the On-Train Data Recorder and is currently analysing this alongside CCTV recordings and signalling data.

This accident took place on the Down Lewes line, where the maximum speed for a train is 70mph. The two Class 387 units on 1F34 were coupled together and were travelling at around 65mph as it approached the point of derailment.

Initial analysis shows that the driver applied the brakes at the point of derailment, and the train began to slow down.

Marks on the rail near the point of derailment are consistent with the wheels of the derailed carriages climbing over the rails.

CCTV images from 1F34 and other services show that track geometry irregularity existed on the approach to the derailment.

The RAIB says that there is also evidence of previous track maintenance activity in the area.

Several reports of rough riding in the area were also received by the RAIB following the accident.

The embankment that the railway runs on is constructed of clay and alluvial/alluvium deposits, both of which the RAIB says are sensitive to variations in the water content.

However, the RAIB says that there is no evidence to indicate that an embankment slip occurred before the accident – although it does say that there is evidence of some previous movement.

The investigation is continuing to look at

• the exact mechanism by which train 1F34 derailed
• the status of the track at this location and how it was inspected and maintained
• the condition of the embankment, including the presence of any coincident risk factors (such as sustained hot weather, nearby structures, and vegetation), and how it was inspected and maintained
• the weather conditions in the area on the day of the accident, and in the weeks and months preceding it
• the effectiveness of any mitigation measures intended to address the risks of operating trains in hot weather
• the condition of train 1F34 and the crashworthiness performance of the rear three vehicles of the train during the derailment
• the emergency response to the accident
• any relevant underlying factors, including any actions taken in response to previous relevant safety recommendations.

The RAIB have released the site back to Network Rail to allow for repairs to take place and the train to be recovery.

Cranes will be needed to lift the carriages away from the railway, before they are moved by road to a secure storage area to make sure that evidence is preserved.

“Following the publication of the Rail Accident Investigation Branch’s (RAIB) investigation update, we remain fully committed to supporting the continuing investigation and acting on any lessons that emerge from its findings.

“We are very sorry that this happened on our railway. Our thoughts remain with everyone affected, especially those who were injured and the family and friends of those on board the train. We also recognise the ongoing impact the incident has had on customers, local communities and railway colleagues.

“Safety is and will always remain our highest priority. While Britain’s railway is one of the safest in the world, when incidents like this occur it is essential that we understand exactly what happened and identify any lessons that can be learned. We will carefully consider any recommendations arising from the investigation and work across the industry to implement them, with the shared goal of making an already safe railway even safer for our customers, colleagues and the communities we serve.

“Given the complexity of the issues being examined, it is important that the independent investigation is allowed to reach its conclusions. We will continue to cooperate fully with the RAIB throughout this process.

“We continue to offer support to our customers and colleagues impacted by the incident. At the same time, our focus remains on keeping people moving while work continues to recover the railway. Our teams at Network Rail and Southern are working closely with industry partners to minimise disruption, provide alternative travel options and keep customers informed about the latest travel arrangements. We are grateful for our customers’ and the Lewes community’s continued patience and understanding while this complex recovery effort continues.

“We would also like to thank our railway colleagues, the emergency services, local authorities and partner organisations whose professionalism and dedication have supported both the immediate response and the ongoing recovery. We are especially grateful to the local community, whose kindness and support towards customers and staff in the immediate aftermath of the accident reflected the very best of Lewes.”

Lucy McAuliffe, Route Director Sussex, Network Rail, and John Whitehurst, Chief Executive Officer at GTR, which operates Southern