A rail track defect existed in the area where a train derailed in East Sussex last week, injuring 30 people, investigators said.

An interim report by the Rail Accident Investigation Branch (RAIB) said CCTV images from preceding services on the line show the fault, which it described as a “track geometry irregularity”.

Preliminary analysis of the derailed train’s onboard data recorder show it was travelling at about 65mph as it approached the point of derailment in Lewes at 3.54pm on August 13.

About 150 people were onboard the eight-carriage Southern train from London Victoria to Eastbourne.

Three carriages ended up on their side, trapping passengers.

A total of 30 people were injured, included 20 who required hospital treatment, the RAIB said.

The RAIB said its investigation will consider the weather conditions on August 13, 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.