British Transport Police officers are appealing for information after a charity worker was attacked at London Bridge Station last month.
Officers have also released CCTV images of a man they would like to speak to in connection with the incident which happened at around 5.30pm on Thursday 17 March.
"The victim, a 29-year-old charity worker from Tower Hamlets, was travelling on the 5.23pm South Bermondsey to London Bridge train when a man approached her and touched one of her legs inappropriately," says PC Mark Payne of BTP's Crime Action Team.
"When the train arrived at London Bridge the woman approached the man and explained that she was unhappy with his behaviour.
"He immediately began shouting and swearing at the victim before slapping her as they left the train, causing her to fall backwards."
As a result of the attack the victim was left with a swollen face and split lip.
PC Payne added: "We've conducted several lines of inquiry into the incident, including taking witness statements, viewing CCTV in the area and circulating images on police intelligence systems, but to no avail so far.
"This was a frightening and intimidating experience for the victim who was simply making her way home from work.
"I am asking anyone who was on the train at the time, or who recognises the man pictured, to come forward and assist our investigation."
Anyone with any information about the incident should contact British Transport Police on 0800 40 50 40 quoting background reference B15/LSA of 7/04/11.
Alternatively call the independent charity Crimestoppers anonymously on 0800 555 111.