At approximately 11.57pm on Saturday 24 July, a 21-year-old woman was having a cigarette on Vernon Walk, opposite the queue for Trilogy nightclub, when she was approached by a man she did not know.
The man put his arm around her waist and grasped her buttock over her clothing. At this point, a group of around five people intervened and the man let go of her.
The man is described as being black, approximately 5ft 11inches tall and of muscular build. He was wearing a long sleeved white shirt and a red cap that was on backwards.
Officers are keen to hear from anyone who may have witnessed the incident and in particular the group of people who intervened and helped the woman.
Were you in the queue for Trilogy nightclub at around midnight? Did you see what happened? Were you one of the group who helped the woman?
Anyone who witnessed the incident or has any information is asked to contact us on 101 quoting 44210294294.
Alternatively people can call Crimestoppers on 0800 555 111 where information can be left anonymously or online at https://orlo.uk/3vT0U
A 34-year-old man from Portsmouth has been arrested on suspicion of sexual assault and fraud by false representation. He has been questioned by officers and released on police bail with conditions.