Transport police have launched an appeal after a man waving a flag reportedly boarded a London Bridge train and threatened a passenger.
British Transport Police said in a statement that they are seeking further information about an incident in which a drunk man began acting aggressively on the train at around 8.30pm on Friday April 12.
The train was headed for Beckenham, in Bromley.
The man was with a woman, said officers, when he reportedly began acting aggressively to passengers while referencing Bloody Sunday.
The name is given to the infamous incident during the Northern Ireland troubles in which the British Army opened fire on civil rights demonstrators in 1972, killing thirteen.
The man is then alleged to have threatened a passenger after being challenged.
Officers said they would like to speak to any witnesses, including one passenger who is thought to have recorded it on her phone.
A man, aged 29 from Beckenham, was arrested on suspicion of nuisance behaviour but has been released while officers carry out further enquiries.
Witnesses can contact BTP by texting 61016 or by calling 0800 40 50 40 and quoting reference 623 of 12/04/19.
Alternatively, Crimestoppers can be contacted anonymously on 0800 555 111.