A politician is demanding an inquiry after a man was almost thrown from a train when the door flew open mid-journey in the Cotswolds.
Gloucester councillor Andrew Gravells was travelling to the city from London on a First Great Western service this month when a door on one of the carriages opened.
The incident happened as the train travelled between Kemble station, near Cirencester, and the station in Stroud.
Mr Gravells said a young passenger tried to get it closed again and was almost thrown from the train as it went through a tunnel.
He said: "If anyone had been stood by the door when it flew open they wouldn't have had a chance of surviving, especially while the train was travelling through the tunnel.
"There should be a trip device in place to stop trains from leaving a station if the door isn't securely locked.
"Luckily nobody was injured this time but if the train had been packed it could have been a different, tragic story."
Mr Gravells said he believed the man in question, who had a lucky escape when he tried to close the door, was called Noel.
He added that after the train stopped and the door was closed again, the driver of the train was forced to walk through a tunnel to get it moving.
He said: "Because the train driver couldn't make contact with the signal operators, he had to leave the train and walk to the end of the tunnel to get the signals altered."
Meanwhile, rail bosses have said they will launch an investigation.
A First Great Western spokesman confirmed the door was left open on the service on December 9.
He said: "This should never have happened and, although no one was injured, we are treating the matter very seriously.
"We've reported the incident to the Office of Rail Regulation and the Rail Accident Investigation Branch.
"When we were alerted to the incident the train was stopped immediately and the door was locked out of use."