Policing.uk
Necessity criteria
- PACE powers
Before a constable may arrest a person without a warrant under section 24 of PACE, two conditions must be met: there must be reasonable grounds to suspect the person is involved in an offence, and the arrest must be necessary for one of the reasons listed in section 24(5), such as to ascertain the person's name, prevent injury, or allow prompt and effective investigation.
In practice
Necessity is not automatic. Simply having reasonable grounds to suspect an offence is not enough. Officers must actively consider which necessity ground applies and be prepared to articulate it. A failure to identify a necessity ground can make an arrest unlawful, even where guilt is later established.
Related terms
Last updated 24 September 2026