A track defect existed in the area where a train derailed near Lewes, East Sussex last week, the Rail Accident Investigation Branch says.

Thirty people were injured, two seriously, when the train came off the tracks on 13 August.

About 150 people were on board the train, which was travelling between Haywards Heath and Lewes.

Network Rail and Southern Rail said three carriages “derailed and slid part-way down the embankment”.

Police declared a major incident as a number of people were trapped inside in scorching temperatures.

A passenger in one of the carriages earlier said that the experience was “completely terrifying”.

“There was a banging. Everything just went topsy-turvy,” said 56-year-old Yana Ludwig, from the United States.

Rob Bradley, who was on board with his young daughter, said that his carriage “jumped upwards” as passengers got thrown forwards.

“The train kind of skidded for quite a while before it stopped.

“Only then, when we turned around, did we see the whole back of the train was open and smoke and dust were pouring into the carriage.”

The Rail Accident Investigation Branch said on Wednesday that rear-facing CCTV images obtained from train services on 13 August showed a “track geometry irregularity” on the “immediate approach to the point of derailment” on the line just outside Lewes Railway Station.

The RAIB also said that there was evidence of previous track maintenance in the area, while it had received several reports of “rough riding” at the derailment location from passengers on other trains.

Thirty people were injured in the incident, according to the RAIB, with 20 requiring hospital treatment, while “significant damage” was caused to the train and railway infrastructure.

The RAIB said that its investigation will consider the weather conditions on 13 August, which were hot and sunny, as well as the status of the track, embankment, condition of the train and the effectiveness of any measures taken to address potential issues caused by hot weather.

The railway line will remain closed for at least another week.

Network Rail and Southern Rail said the carriages that slid down the embankment will “need to be carefully lifted away by crane”.

They said that the location makes this “particularly difficult” as the railway is close to a river, in a site of special scientific interest, and restricted road access was via a residential area.

Once the train has been removed, engineers will be able to assess the damage to the railway and “understand the scale of the repair work needed before services can resume safely”.

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