Martin Frobisher, of Network Rail, said the summer’s hot weather had “presented exceptional challenges to the railway”.
In an interview with the Transport Correspondent Katy Austin, Frobisher also confirmed speed restrictions were not in place in either Wickford or Lewes.
On the possible impact of the hot weather, he said “yes, that’s one of the things that we’re looking at.
“We’ve got our investigations underway. We’ve got technical engineers on site, our best experts who are on site with the Rail Accident Investigation Branch.
“They’re looking very thoroughly at what’s happened. And based on that, we will act on what we learn.”
However, he added it was “too early to speculate on the full findings”.
The investigation would specifically assess “whether or not this was weather-related”, said Mark Francois, the Conservative MP for Rayleigh and Wickford.
The Department for Transport stressed Britain’s railways were “among the safest in the world” as it reacted to the incident.
It said derailments were “incredibly rare” events.
An East of England Ambulance Service spokesperson said: “Our crews assessed 62 patients who were on board the train.
“Following assessment, all patients were discharged at the scene.
“We also assisted with the evacuation of a second train that was unable to continue its journey due to the derailment.
“There were no casualties among those on board.”
A spokesperson for BTP also confirmed there were no reported injuries.
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