Chief police officer is a phrase used in the United Kingdom to describe the position held by the most senior police officer in a police force. It refers to either one of the 53 Chief Constables, the Commissioner of the City of London Police or the Commissioner of the Metropolitan Police. Such police officers are members of the Association of Chief Police Officers. The phrase is used in legislation when giving powers such as those to permit public processions, or grant firearms licenses. Some such activities can usually be delegated to any constable.
Chief officer rank
Officers holding the ranks of assistant chief constable, deputy chief constable, chief constable, and those holding the following ranks in either the Metropolitan Police Service or City of London Police: commander, deputy assistant commissioner, assistant commissioner, the deputy commissioner and the commissioner are also members of ACPO and are usually referred to as being of "chief officer" rank.