The incident happened at 9.47pm on Friday, 13 April.

The victim, a woman aged 21, was boarding a Southbound Victoria line train with a friend when they witnessed an assault by a large group of teenagers on a man.

The woman and her friend followed the group and confronted them on their behaviour.

During the exchange, the victim began filming several members of the group. A member of the teenage group noticed this and assaulted the woman.

The victim suffered reddening to the skin on the side of her face and had large amounts of her hair pulled out.

Officers would like to speak with the woman shown in the CCTV images as she may have information which could help with the investigation.

If you recognise them, or have any other information about the incident, please call BTP on 0800 40 50 40 or text 61016, quoting reference 408 of 25/04/2018.