An explosion on board a passenger train had "caused considerable damage," the investigators say.
According to a spokesman, the empty train left Central Rivers' service depot in Burton-upon-Trent when electrical equipment exploded on board a bus cabinet.
It was only discovered when the driver drove by train to change trains at Birmingham New Street Station.
The incident is being investigated by the rail accident investigation department.
It happened aboard a CrossCountry service on September 26 at around 6:00 am CET.
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The operator said the cause had been "quickly identified" and minor changes had been made to similar features.
Tom Joyner, Managing Director of CrossCountry, said, "The safety of our customers and employees is our highest priority, and we are grateful to our engineers and maintenance companies for making sure that this can not happen again."
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