Police are appealing for witnesses to come forward after an elderly man was assaulted by another passenger at the ticket barriers on Waterloo Station.
Detectives have released CCTV images of a man they would like to speak to about the incident which took place just before 7pm on Wednesday 5 November.
Detective Constable Rachel Smith said: "The victim, a 74-year-old man from Southampton, who was walking with the assistance of a stick, had been queuing at the barriers of platform 11 when a man barged his shoulder from behind.
"As the victim stumbled and shouted to the man, the man turned and punched him in the chest before hurrying through the barriers towards his train."
DC Smith continued: "This was an unprovoked attack on a man who was simply going about his journey.
"As part of the investigation, we are releasing CCTV images of a man we would like to speak to, as we believe he may hold vital information about what took place.
"Did you see the incident happen? Do you recognise the man pictured? Are you the man himself? If so, we would like to speak to you."
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference SSUB/B13 of 27/11/14. Information can also be passed anonymously to independent charity Crimestoppers on 0800 555 111.