A 12-year-old child was reportedly punched in the face on an “extremely busy” train travelling towards Waterloo.
Officers said the frightening attack happened on Thursday night at about 8.30pm, when the capital faced a day of rail chaos because of the heat.
British Transport Police said a 28-year-old man, from Greenhithe, was removed from the train at Waterloo East and arrested on suspicion of assault, being drunk and disorderly and affray. He remains in police custody this morning.
The force said: “The man began to behave threateningly to other passengers as the 8.32pm Charing Cross to Gravesend service left platform 5.
“His behaviour became increasingly more aggressive and he is then reported to have punched a child, thought to be around 12 years of age, who officers are now trying to trace.”
British Transport Police Sergeant Tom Gallagher said: “I would ask anyone who witnessed this man’s behaviour and the reported assault on the child to please get in touch with us as soon as they can today to provide an account.
“The train was extremely busy and we believe many people helped to restrain him at the time who have not yet spoken to police.
“In particular, I would like to urge the victim of the assault, or their parents, to come forward and assist us with our enquiries. As you’ll imagine we are very concerned about the impact this incident could have had on them and we’d like to check on their welfare as soon as possible.”
Anyone with information can contact BTP by texting 61016 or calling 0800 40 50 40quoting reference 635 of 25/07/19.