Police were called at around 5.20am on Sunday 20 February to reports that a 38-year-old woman had been sexually assaulted on a walkway off Queen Street, shortly after leaving a nearby nightclub.
Police have issued a CCTV appeal and believe the man in the images was in the area at the time and may be able to assist with their enquiries.
Detective Sergeant Simon Coates, of Lancaster Police, said: “We received reports this morning that a woman had suffered a sexual assault and we are now working extremely hard to piece together exactly what occurred.
“We believe the man in the CCTV pictures may be able to assist with our investigation and we would urge him, or anybody who thinks they know who he is, to contact us as soon as they can.”
Anybody with information is asked to contact police on 101, quoting log number 298 of today (February 19th).