A man wearing a penguin costume and his father were assaulted on a train to Chelmsford, in a row which appears to have been sparked by football.
Officers have released CCTV images in connection with the assault and affray, and are appealing for information about those caught on film.
The incident happened between 11.50pm and 12.25am on 21 December, on board the Liverpool Street to Chelmsford service.
A group of around six men were sitting near the train toilet and one of them asked another passenger, a 19-year-old man who was waiting outside the toilet, if he supported Tottenham Hotspur.
The passenger, who was dressed in a fancy dress penguin costume, used the toilet and when he came out, he found the group of men blocking his route back to his seat and being aggressive towards him.
The victim’s father, a 56-year-old man, approached the group and tried to pull the victim away, at which point they were both assaulted by the group, who punched and kicked the father and son.
The disorder spilled out on to the platform at Chelmsford station.
Another member of the public attended to intervene and was also assaulted, sustaining a black eye. The original two victims sustained multiple cuts and bruises to their faces and bodies.
Officers would like to speak to the people shown in the CCTV images as they may have information which could help the investigation.
If you recognise them, or have any other information which could help, please call BTP on 0800 40 50 40 or text 61016, reference number 228 of 9 January 2018.