Train investigators looking into last week's derailment in Lewes have said an "irregularity" existed on the approach to the site where the accident took place.
The Rail Accident Investigation Branch says the "track geometry irregularity" was visible in CCTV images taken immediately before the derailment in East Sussex.
It attached an image to the report taken from a train moving in the opposite direction showing the irregularity.
Around 150 people were on the train when it derailed, the report says, adding that 30 people were injured in the accident, with 20 people requiring hospital treatment, some with serious injuries.
Significant damage was also caused to the train and to railway infrastructure.
Investigators said the railway embankment at the site was constructed of material that can be sensitive to changes in water content.
However, the report added: "Although, at this stage, there is no evidence to indicate that a significant embankment slip occurred before the accident, there is evidence that some movement had previously taken place."
The accident happened during a period of sustained high temperatures in the UK.
The ongoing investigation will consider factors including "the effectiveness of any hot weather mitigation and the condition of the train, track and embankment".
A full report will be published once the investigation is complete.
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(c) Sky News 2026: Track 'irregularity' found at site of Lewes train derailment, report says
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