In relation to the need for reasonable suspicion, there is no

requirement for the police to have anything like a prima facie case and

they need not explore every explanation before making the arrest

(Castorini v. Chief Constable of Surrey (1988)). The emphasis is upon

suspicion, for example that an arrestable offence has been committed,

and not evidence. It is the purpose of detention which is important

and not whether the individual is later charged. Under the ECHR,

Art. 5 (1) (c) recognises ’reasonable suspicion’ as a ground for arrest

and this, as with the national law, involves an honest belief and

objective evaluation on the part of the police: Fox v. UK (1990). It is to

be appreciated, however, that even under the Convention, terrorist

offences fall into a special category with reduced safeguards. It is for

the court to subsequently determine whether the officer had sufficient

Information available, upon which to make his suspicion reasonable,

at the time of the arrest. The suspicion may be thin and yet still be

sufficient (Ward v. Chief Constable of Avon (1986)) and can be based

solely on the words of an informant (James v. Chief Constable of

South Wales (1991)). A remote possibility, however, will not suffice

(Chapman v. DPP (1988)) and when an arrest is premature (i.e. without

reasonable grounds) it is unlawful (Plange v. Chief Constable of South

Humberside (1992)). The term ‘reasonable’ imposes an objective yard-

stick. In Bull v. Chief Constable of Sussex (1995) it was said that

the test is what the reasonable person who knows both the law and the

facts of the case would believe at the material time. The suspicion

must, therefore, be based on information known to the officer at the

material time (O’Hara v. Chief Constable of the RUC (1997)).

Once the suspicion arises, the officer must also exercise his executive

discretion in accordance with the general principles of administrative

law (i.e. Wednesbury reasonableness) so as not to constitute an ultra

vires abuse of power. The exercise of this discretion could be challenged

if the police do not make full enquiries before the arrest (see Castorini

(1988)). Nevertheless, this appears not to unduly fetter the actions of

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Police Powers of Arrest and Search in the Investigation of Crime

the police. In Mohamed-Holgate v. Duke (1984), for example, an officer

exercised his discretion to arrest someone he reasonably suspected,

solely motivated by the psychology that the suspect was more likely to

confess if detained in custody. This was held by the House of Lords

to be a ‘Wednesbury’ reasonable exercise of the power to arrest, and

confirms that arrest is validly part of the investigative process.

(ii) For any offence

The Act offers the police (but not the citizen) a novel and general power

of arrest for any non-arrestable offence (normally of a less serious

nature than an arrestable offence) where one of the specified ‘general

arrest conditions’ is satisfied and where the service of a summons (which

on average takes 88 days) is impracticable or inappropriate (s. 25 (1)).

Accordingly, and unlike arrestable offences, non-arrestable offences

are deemed insufficiently serious to justify the arrest of those who are

simply suspected of having committed them, and other circumstances

are necessary before an arrest can be made. The officer, moreover, must

have reasonable grounds for suspecting both that a non-arrestable

offence has been (or is being) committed or attempted and that the

person arrested is the offender. This suspicion, seemingly, must arise

before the general arrest conditions become relevant: G v. DPP (1989).

The general arrest conditions are listed in s. 25 (3) as being where the

name of the suspect is unknown, cannot be ascertained or is doubted;

where a satisfactory address has not been furnished; where the suspect

needs to be restrained so as to prevent either harm to himself or a third

party, physical injury to himself, loss or damage to property, an offence

against public decency or an obstruction of the highway; or where an

arrest is appropriate in order to protect a child or other vulnerable

person from the suspect. Many of the above conditions are dependent

upon the officer having reasonable grounds to doubt the suspect or to

believe that the specified consequence will occur. The purpose of s. 25 is

to widen the power of summary arrest potentially to cover all offences

(e.g. riding a bicycle along a public road in a dangerous manner:

Nicholas v. Parsonage (1987)) and not wearing a seat belt: Ghafar v.

Chief Constable of West Midlands Police (2000)). As well as the ground

of arrest, the suspect must also be told of the general arrest condition

relied on by the police.

(iii) For fingerprinting

Certain offenders may be required to attend a police station so that

fingerprints may be taken (s. 27). If a person fails to comply, any