PACE, as amended by the Serious Organised Crime and Police Act 2005, establishes a complex framework of factors that police officers must consider during arrest decision making. Officers must possess a reason to arrest, it must be necessary to arrest for that reason, and they must give at least a 'cursory consideration' to alternatives. Based on a four-year ethnographic study of frontline officers from two forces in Northern England, we argue that the 2005 reforms have not achieved their aims. The new regime tasks officers with undertaking a complex legal assessment prior to arrest, but officers are often confused about the necessity criteria which, moreover, is typically a minor consideration in contrast to demanding practical and policy pressures. This means that unlawful and non-human-rights-compliant arrests continue to be regularly made and, equally significantly, many suspects are escaping the criminal justice system because officers are not considering arrest alternatives.