Detectives investigating an assault at London Bridge Station have released a CCTV image of a man they wish to speak to.
A 39-year-old man was headbutted at London Bridge Station shortly after midnight on Wednesday 9 December 2015.
Detective Constable Steve Ajayi said: "The victim was attacked on the station concourse by a man who was unhappy about music being played on the victim's friend's phone.
"He was headbutted, sustaining a cut to his nose."
Following the assault, the attacker left the station.
Officers have analysed CCTV of the incident and spoken to witnesses.
DC Ajayi added: "There is no excuse for such violent behaviour and we need people to help us find the person responsible.
"I am confident the man in the image will be able to assist with our investigation. Know him? We want to hear from you."
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference SSUB/B11 of 11/01/16. Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111.