A man spat in a woman’s face and began pushing her on the Tube after she objected to him having sex in a Northern line carriage.
British Transport Police (BTP) have launched an appeal for information after the woman was attacked shortly before 1am on January 14 as the train neared Kennington station.
BTP said the victim had “approached a man and woman engaged in a sexual activity and challenged them to stop”.
It added: “The man then stood up and became aggressive, spitting at her and pushing her.”
Other passengers are then thought to have intervened to break up the altercation, the Evening Standard reported.
Investigating officer PC Suleman Yazdani, said the couple were engaged in “highly inappropriate behaviour”.
Of the attack, Yazdani said: “The woman was simply asking this couple to stop, there was no need for aggression.
“If you were on that train or saw anybody acting suspiciously I would urge you to contact us as soon as possible.
“Any information, no matter how small, could be vital to our investigation.”
Anyone with information on the incident is urged to contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 13 of 14/01/2017. Alternatively, people can contact Crimestoppers anonymously on 0800 555 111.