Officers from the Met's Roads and Transport Policing Command (RTPC) are appealing for witnesses after a man was racially abused on a bus.
The investigation was launched after a video of the incident circulated on social media, and was reported in the press.
The video shows a women arguing with a man, and using racist language.
The incident is believed to have happened on a 195 in the Hayes area of Hillingdon borough, on Saturday, 14 September.
Officers want witnesses to the incident, or anyone who can provide information about the people involved to come forward.
Initial enquiries have been made with the bus company.
If you have any information about the incident, please call 101 quoting 0921546/19, or Crimestoppers anonymously on 0800 555 111.