Officers are appealing for information after a woman was spat at on board a Northern Underground train.
The incident occurred on board a Euston to Edgware train on Saturday 25 August.
At approximately 7.15pm, a woman boarded the train at Hendon station and started to shout at passengers on the train.
She then began shouting at the victim, a 26-year-old woman. In response to this attack, the victim moved to a different part of the carriage.
However, as she was walking away, the woman verbally abused her and spat on her cheek.
Members of the public intervened and separated the victim from the woman.
Both the suspect and victim alighted at Edgware.
The woman is described as being white, 5ft 4inches, aged mid-thirties, with a slim build. She was also wearing pink lipstick and had short brown hair shaved at both sides.
Officers are looking to speak with anyone who may have been on board the train or at the station at the time of the incident.
Anyone with information which could help with the investigation is asked to contact British Transport Police by calling 0800 40 50 40 or texting 61016 with reference 176 of 27 August.