<Li> causing an unlawful obstruction of the highway . </Li> <Li> to protect a child or other vulnerable person from the person in question, </Li> <Li> to allow the prompt and effective investigation of the offence or of the conduct of the person in question, </Li> <Li> to prevent any prosecution for the offence from being hindered by the disappearance of the person in question . </Li>

When can an arrest be made without a warrant