Police intercepted a train in Chorley after a man was said to be abusive and threatening towards a female passenger.
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The woman alerted police using their non-emergency text messaging system 61016 which allows passengers to discreetly alert police to a non-emergency crime.
Officers were notified of the incident which started on the train travelling from Manchester just before 7pm on October 11.
A spokesman said: "We received a text message to say that a passenger had been abusive and threatening to a woman on the train.
"This information was then passed on to our control room who boarded the train at Chorley.
"Officers spoke to the woman and our enquiries into the incident are on-going.
"You can text us on 61016 to report non-emergency incidents, similar to the ones you would report to the 101 phone number provided by your local police force.
"The text number is monitored 24/7 and, while it is not for reporting emergencies, we will be able to send officers if required."
Nobody has been arrested in connection with the incident.
Anybody who witnessed the incident is asked to contact police on 101 quoting log reference 498 of October 11.