A man who suffered facial injuries outside Liquid nightclub in Windsor has complained to police about the incident.
His action has led the force to refer the matter that took place on December 17 at 3.11am to the Independent Police Complaints Commission (IPCC), who is now investigating.
Officers carried out an arrest on a 19-year-old man on suspicion of being drunk and disorderly outside the William Street venue.
Police are appealing for witnesses in connection with the incident and have released a CCTV image of people that saw it and is urging them to talk about the night.
Detective Chief Inspector Yvette Hitch, from the police's professional standards department, said it shows a number of people, who will be able to provide 'valuable information'.
Anyone with information should call Det Ch Insp Hitch via 24-hour police enquiry line 101.
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