The incident took place between 9pm and 9.15pm on Thursday, July 3 when a 28-year-old woman was followed along Abington Street to the bus station.
She was then forced into an alcove and pinned up against the wall. The offender tried to kiss the victim, who managed to escape.
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The offender is aged 27 to 33, 5ft 8in to 5ft 10in and white. He is of medium build, with short black hair and was clean shaven. He wore a brown jacket with a cream top and jeans.
Police officers are currently investigating whether the incident is linked to the two other assaults which recently took place close by.
The victim only came forward in the last few days.
Witnesses can call police on 08453 700700 or Crimestoppers, anonymously, on 0800 555111.
