Police involvement in the prosecutional system is analyzed. The picture that emerges is one of extremes with England and Wales at one end (wide discretion and considerable employment of police advocates) and Scotland at the other (theoretically no prosecutorial discretion and no use of police advocates). Northern Ireland theoretically falls somewhere in between, although in practice it tends more to the English position. All three systems operate effectively in practice; nevertheless, there is a call for the reform of the systems in England and N. Ireland, based essentially on a curtailment of police discretion and the withdrawal as advocates from the courts. The case of police prosecutorial discretion has been examined more thoroughly than that of police advocacy principally because it is the more controversial aspect at the present time. The argument is made, though, for the police as repositories of the discretion to prosecute. In the United Kingdom, to an extent unique in the world, the police are not feared but are respected. The position which they hold and the functions which they discharge must be properly understood as an essential prerequisite to a proper evaluation of where prosecutorial discretion should be located. Chapter notes are provided. (Author abstract modified).