On 13 August 2026, Southern service 1F34 was approaching Lewes when the rear three vehicles of the eight-car train derailed and overturned on the railway embankment.

A week on, the Rail Accident Investigation Branch has released an update providing our first detailed insight into what happened — and in this flash briefing, we take a look at what we know so far.

We’ll examine the track geometry irregularity identified immediately before the derailment, reports of rough riding from other trains, the condition of the embankment, the exceptionally hot and dry weather, and the evidence RAIB is now analysing.

Importantly, this isn’t about deciding what caused the accident, this is a snapshot of what we know, what we don’t yet know, and what the investigation will be looking at next.

OPENING CREDITS

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