Here is what the law says :
2 Elements of Arrest under section 24 PACE
2.1 A lawful arrest requires two elements:
A person’s involvement or suspected involvement or attempted involvement in the
commission of a criminal offence;
AND
Reasonable grounds for believing that the person’s arrest is necessary.
Necessity criteria
2.4 The power of arrest is only exercisable if the constable has reasonable grounds for
believing that it is necessary to arrest the person. The criteria for what may constitute
necessity are set out in paragraph 2.9. It remains an operational decision at the
discretion of the arresting officer as to:
• what action he or she may take at the point of contact with the individual;
• the necessity criterion or criteria (if any) which applies to the individual; and
• whether to arrest, report for summons, grant street bail, issue a fixed penalty
notice or take any other action that is open to the officer.
2.5 In applying the criteria, the arresting officer has to be satisfied that at least one of the
reasons supporting the need for arrest is satisfied.
2.6 Extending the power of arrest to all offences provides a constable with the ability to
use that power to deal with any situation. However applying the necessity criteria
requires the constable to examine and justify the reason or reasons why a person
needs to be taken to a police station for the custody officer to decide whether the
person should be placed in police detention.
2.7 The criteria below are set out in section 24 of PACE as substituted by section 110 of
the Serious Organised Crime and Police Act 2005. The criteria are exhaustive.
However, the circumstances that may satisfy those criteria remain a matter for the
operational discretion of individual officers. Some examples are given below of what
those circumstances may be.
2.8 In considering the individual circumstances, the constable must take into account the
situation of the victim, the nature of the offence, the circumstances of the suspect and
the needs of the investigative process.
The criteria are that the arrest is necessary:
(c) to prevent the person in question –
(i) causing physical injury to himself or any other person;
(ii) suffering physical injury ;
(iii) causing loss or damage to property;
(iv) committing an offence against public decency (only applies where
members of the public going about their normal business cannot
reasonably be expected to avoid the person in question); or
(v) causing an unlawful obstruction of the highway;