A woman was approached by a man at the station who engaged her in a conversation just before 4pm on June 14.
He then followed her through the station before sexually assaulting her as she went up the stairs.
Officers believe the man in the image may have information which could help their investigation.
Anyone who recognises him is asked to contact BTP by texting 61016 or by calling 0800 40 50 40, quoting reference 460 of 14 June.
Alternatively, you can contact Crimestoppers anonymously on 0800 555 111.
