Having now had time for things to calm down the next check and balance requires an independent reassessment of the evidence to correct any unlawful arrests… This naturally increases the ‘thresh hold to remove another’s liberties!

As guilt is proven in court, innocence prevails creating the duty that detention is a last resort, and all other options must be exhausted!

Importantly you must understand the abuses under the most commonly cited reasons to detain:

Limb 1: To secure or preserve evidence relating to an offence for which the person is under arrest.

Limb 2: To obtain such evidence by questioning the person.

to allow prompt investigation

The Test for Authorising Pre-Charge Detention under PACE Section 37(3)

1. Introduction

1.1 The Role of the Custody Officer

The Police and Criminal Evidence Act 1984 (PACE) established the statutory role of the Custody Officer, typically a police sergeant, who holds distinct responsibilities at designated police stations.1 Appointed under Section 36 of PACE, the Custody Officer is fundamentally responsible for overseeing the treatment and welfare of all persons detained at that station, ensuring compliance with the provisions of PACE and its associated Codes of Practice.3 This includes safeguarding the detainee’s rights and ensuring all required matters are recorded accurately in the custody record.3

A crucial aspect of this role is the requirement for independence from the ongoing investigation of the offence for which the person was arrested.3 The Custody Officer acts as an independent gatekeeper, responsible for authorising or refusing detention and ensuring that any detention is lawful and justified according to the strict criteria laid down in PACE.3 This separation is designed to provide a check on police powers and protect the rights of the arrested individual.7

1.2 The Post-Arrest Decision Point

Upon an individual’s arrival at a police station following arrest (or upon their arrest at the station itself), the Custody Officer faces an immediate and critical decision point. Section 37(1) of PACE imposes a duty on the Custody Officer to determine, as soon as practicable, whether they have sufficient evidence before them to charge that person with the offence for which they were arrested.8 The Act permits the Custody Officer to detain the individual for such period as is necessary to enable this determination to be made.8

Following this initial assessment, several outcomes are possible under Section 37:

• If sufficient evidence exists, the person may be charged (Section 37(7)(a)).8
• If sufficient evidence exists but a charging decision requires referral to the Crown Prosecution Service (CPS), the person may be released on bail or kept in detention pending that decision (Section 37(7)(a) as amended, linking to Section 37B).9
• If sufficient evidence exists but the Custody Officer decides against charging (and the matter doesn’t require CPS referral), the person must be released, potentially on bail (Section 37(7)(b)/(c)).9
• If the Custody Officer determines there is not sufficient evidence to charge, the default position is release, either on bail or without bail (Sections 37(2) and 37(2A)).8
• Crucially, even if there is insufficient evidence to charge, the Custody Officer may authorise continued detention if specific conditions relating to the necessity of securing, preserving, or obtaining evidence are met (Section 37(3)).8

1.3 Purpose and Structure of the Report

This report provides an expert legal analysis of the specific test outlined in Section 37(3) of PACE 1984. This provision permits a Custody Officer to authorise the detention of an arrested person before charge, even when the threshold of “sufficient evidence to charge” under Section 37(1) has not been met. The analysis will examine the legal framework governing this power, dissect the components of the “necessity” test, explore its interpretation through relevant case law and official guidance, and detail the associated procedural requirements and safeguards. The structure will follow the logical progression of the Custody Officer’s decision-making process under Section 37.

2. The Initial Assessment: Sufficient Evidence to Charge (PACE S37(1))

2.1 The Primary Duty

The foundational duty of the Custody Officer upon encountering an arrested person is prescribed by PACE Section 37(1). This section mandates that the Custody Officer “shall determine whether he has before him sufficient evidence to charge that person with the offence for which he was arrested”.8 This determination must be carried out “as soon as practicable” after the person’s arrival at the station or after their arrest within the station.8 To facilitate this crucial assessment, Section 37(1) explicitly allows the Custody Officer to “detain him at the police station for such period as is necessary to enable him to do so”.8 This initial period of detention is therefore specifically linked to the task of evaluating the available evidence against the charging standard.

2.2 Defining “Sufficient Evidence”

PACE Section 37 does not explicitly define the standard of “sufficient evidence to charge”. However, it is generally understood within the criminal justice system to align with the standard required by the Code for Crown Prosecutors for bringing a charge. This typically involves the Full Code Test, which requires both an evidential stage (is there enough evidence for a ‘realistic prospect of conviction’?) and a public interest stage. While the Custody Officer applies the evidential test, the ultimate decision, particularly in more complex or serious cases, may rest with the CPS.13

Section 37B of PACE outlines the procedure when a Custody Officer determines that there is sufficient evidence according to their assessment, but the case requires referral to the Director of Public Prosecutions (DPP) via the CPS for a formal charging decision.1 In such instances, the person may be released on bail or kept in detention under Section 37(7)(a) specifically “for the purpose of enabling the Director of Public Prosecutions to make a decision under section 37B”.9 This highlights that the Custody Officer’s initial assessment of sufficiency under S37(1) is a distinct step, although potentially leading to a CPS decision under S37B. Guidance issued by the DPP under Section 37A assists Custody Officers in determining how to deal with persons under Section 37(7), including when referral to the CPS is appropriate.1

2.3 Outcome if Evidence is Sufficient

If the Custody Officer determines, pursuant to Section 37(1), that sufficient evidence is present, the subsequent actions are governed by Section 37(7). The person must either be charged with the offence or released.8 As noted above, release under Section 37(7) can occur without charge but potentially on bail, either because the CPS needs to make the final decision (S37(7)(a) linking to S37B) or for other reasons determined by the Custody Officer (S37(7)(b) or (c)).9 Detention cannot lawfully continue simply because evidence is sufficient; a decision to charge or release (potentially pending CPS decision) must follow.

3. Insufficient Evidence: Release as the Default (PACE S37(2) & S37(2A))

3.1 The Presumption of Release

Where the Custody Officer, having reviewed the available information, determines under Section 37(1) that there is not sufficient evidence to charge the arrested person, PACE establishes a clear presumption in favour of release. Sections 37(2) and 37(2A), as amended, mandate that the person must be released.8 This release is conditional on whether the pre-conditions for bail are satisfied:

• If the pre-conditions for bail are satisfied, the person must be released on bail (Section 37(2)).9
• If the pre-conditions for bail are not satisfied, the person must be released without bail (Section 37(2A)).9

This statutory structure underscores a fundamental principle of PACE: detention following arrest, particularly when the evidence does not meet the charging standard, is the exception rather than the rule. Liberty should be restored unless there is a specific, legally defined justification for continued deprivation.4 The power to authorise detention under Section 37(3) operates as a specific carve-out from this default position of release.

3.2 Bail Considerations (Brief Overview)

The decision to grant pre-charge bail under Section 37(2) (or other relevant sections like S34(5)) involves separate considerations, primarily focused on managing risks associated with the suspect’s release pending further investigation.13 Statutory guidance and recent legislative changes (Police, Crime, Sentencing and Courts Act 2022) emphasise that pre-charge bail should be considered where necessary and proportionate, removing a previous presumption against its use.5 Factors influencing the bail decision and the imposition of conditions often relate to ensuring the suspect surrenders to custody later, preventing further offending, preventing interference with witnesses or the investigation, or protecting victims.14 While a detailed examination of bail law is beyond this report’s scope, understanding that release (often on bail) is the primary alternative when evidence is insufficient provides essential context for the exceptional nature of authorising detention under Section 37(3).

4. The Exception: Authorising Detention Without Sufficient Evidence (PACE S37(3))

4.1 The Statutory Power

PACE Section 37(3) provides the specific and limited legal basis upon which a Custody Officer may authorise the continued detention of an arrested person when the Section 37(1) threshold – sufficient evidence to charge – has not been met. The subsection states:

“If the custody officer has reasonable grounds for believing that [the person’s] detention without being charged is necessary to secure or preserve evidence relating to an offence for which the person is under arrest or to obtain such evidence by questioning the person, he may authorise the person arrested to be kept in police detention.” 8

This power is discretionary (“may authorise”) but is strictly conditional upon the Custody Officer having “reasonable grounds for believing” that detention is “necessary” for one of the two specified purposes. It is the sole justification for pre-charge detention in the absence of sufficient charging evidence.

4.2 The Two Permitted Purposes

Section 37(3) permits detention only if it is necessary for one or both of the following purposes:

• Limb 1: To secure or preserve evidence relating to an offence for which the person is under arrest. This limb concerns the protection of existing evidence from being lost, destroyed, damaged, contaminated, or otherwise interfered with. Examples could include situations where detention is deemed necessary to allow officers time to conduct searches of the person or premises linked to them, to seize relevant items (e.g., clothing, digital devices, weapons), to prevent the suspect from alerting co-conspirators who might destroy evidence, or to preserve forensic evidence on the suspect’s person or belongings.9
• Limb 2: To obtain such evidence by questioning the person. This limb relates directly to the need to conduct an interview with the suspect.9 The justification here is that questioning the individual is essential to gather information or an account that constitutes evidence relevant to the offence, which is not currently available or sufficient for a charge. This is often invoked when the suspect’s account is considered crucial to progressing the investigation.

4.3 The Custody Officer’s Independent Decision

The authority to permit detention under Section 37(3) rests exclusively with the Custody Officer.2 This decision must be an independent exercise of judgment, separate and distinct from the arresting officer’s justification for the initial arrest under PACE Section 24.5 While the reasons for arrest (reasonable suspicion of an offence and necessity for arrest) provide the context, the Custody Officer must make a fresh assessment based on the specific requirements of Section 37(3) – whether continued detention is necessary for the specified evidence-related purposes.5

The Custody Officer is required to personally consider the grounds presented by the arresting officer, potentially gather further information, and allow the suspect or their representative to make representations before making their decision.5 College of Policing Authorised Professional Practice (APP) guidance explicitly states that the decision to detain should not be a mere “rubber-stamping” of the arrest but an independent determination, viewing detention as a “last resort”.5

The decision point governed by Section 37(3) serves as a critical control mechanism within the PACE framework. Following the initial steps where the Custody Officer assesses the sufficiency of evidence (S37(1)) and where release is mandated if evidence is insufficient (S37(2)/(2A)), Section 37(3) provides a specific, narrowly defined exception. This exception permits detention only where it is demonstrably necessary for securing, preserving, or obtaining evidence. This structure is intended to act as a significant procedural safeguard, preventing the unnecessary deprivation of liberty solely on the basis of suspicion when the state lacks sufficient evidence to proceed with a charge. However, the practical effectiveness of this safeguard depends entirely on the Custody Officer rigorously and independently applying the ‘necessity’ test as interpreted by law and guidance. There is a recognised tension between the pressures of investigation and the duty to protect liberty at this gateway stage. Research has suggested that, in practice, Custody Officers may sometimes feel pressure to facilitate the investigation rather than acting purely as an independent check, potentially weakening this safeguard.7 This highlights the crucial importance of clear guidance, robust training, and potentially enhanced supervision or quality assurance mechanisms to ensure the high threshold for detention under S37(3) is consistently and lawfully applied.6

5. Deconstructing the Threshold: “Reasonable Grounds” and “Necessary”

The authorisation of detention under PACE Section 37(3) hinges on two key elements: the Custody Officer must have “reasonable grounds for believing” that detention is “necessary” for one of the specified purposes.

5.1 “Reasonable Grounds for Believing”

This phrase establishes the standard of justification required for the Custody Officer’s belief. It demands more than subjective opinion, hunch, or mere suspicion. There must be an objective basis for the belief, rooted in ascertainable facts or credible information available to the Custody Officer at the time the decision is made. The test incorporates both subjective and objective elements: the Custody Officer must genuinely hold the belief (subjective), and that belief must be one that a reasonable person, possessed of the same information, could also reasonably hold (objective). This standard mirrors the threshold required for reasonable suspicion justifying an arrest under PACE Section 24.

5.2 Defining “Necessary”: The Core of the Test

The word “necessary” is the cornerstone of the Section 37(3) test and imposes a high threshold for authorising detention.

• Statutory Interpretation: The plain meaning of “necessary” implies something that is required or indispensable, not merely something that is helpful, convenient, expedient, or desirable.19
• PACE Code C Guidance: While Code C (the Code of Practice for the Detention, Treatment and Questioning of Persons by Police Officers) does not provide a specific definition of “necessary” within the context of S37(3), its overarching principles reinforce the requirement for strict justification. Paragraph 1.1 mandates that “All persons in custody must be dealt with expeditiously, and released as soon as the need for detention no longer applies”.4 This principle permeates the Code and supports a restrictive interpretation of powers that deprive individuals of liberty.16
• College of Policing APP Guidance: The Authorised Professional Practice (APP) on Detention and Custody provides more explicit guidance. It stresses that detention is always the “last resort”.5 Custody Officers are instructed to authorise detention “only when it is necessary to detain rather than when it is convenient or expedient”.5 The APP explicitly separates the necessity test for detention from the necessity test for arrest, emphasizing the Custody Officer’s independent assessment.5 Furthermore, any detention must be proportionate to the legitimate aims pursued.5

5.3 Judicial Interpretation – The High Bar for Necessity

Case law, primarily interpreting the parallel “necessity” requirement for arrest under PACE Section 24(5), provides crucial guidance on how this term should be applied in the context of detention decisions under Section 37(3).

• The Hayes Two-Stage Test: The Court of Appeal in Hayes v Chief Constable of Merseyside Police 1 WLR 517 established the authoritative two-stage test for assessing the necessity of an arrest.19 Although concerning arrest, its principles are directly applicable to the Custody Officer’s assessment under S37(3):

1. Subjective Stage: Did the officer (in the S37(3) context, the Custody Officer) actually believe that detention was necessary for one of the specified purposes (securing/preserving evidence or obtaining it by questioning)?
2. Objective Stage: Was that belief objectively reasonable, assessed based on the information known to the officer at the time the decision was made?

• Analysis of Key Case Law: Several key cases illustrate the courts’ approach to the objective limb of the necessity test:

• R (TL) v Chief Constable of Surrey Police EWHC 129 (Admin): This case, concerning the necessity of arrest, underscored the importance of considering voluntary attendance for an interview as a practicable alternative. If a suspect indicates willingness to attend voluntarily, and there are no objective reasons to doubt this, arrest solely for the purpose of interview may not be deemed necessary. This principle logically extends to the S37(3) assessment: if evidence can be obtained via questioning through a voluntary interview arranged after release, continued detention may not be objectively necessary for that purpose.20
• McCollum & Others v Chief Constable of the Police Service of Northern Ireland NIQB 17 (The ‘Bloody Sunday’ Investigation Case): The Police Service of Northern Ireland (PSNI) sought to arrest former soldiers in England and Wales to transport them to Northern Ireland for interviews related to the Bloody Sunday investigation.19 The High Court in Northern Ireland held that the arrests were not necessary.19 A key factor was the soldiers’ explicit offer to attend interviews voluntarily at police stations in England or Wales; this offer effectively negated the necessity of arrest for interview purposes.19 The court rejected PSNI’s arguments based on administrative convenience or perceived effectiveness (e.g., needing to show hard copy documents located in NI when electronic copies were available and could be shown elsewhere).19 Lord Thomas stated clearly that necessity requires “more than merely desirable or more convenient to the arresting authority”.19 This case strongly reinforces that the availability of less intrusive, yet practicable, alternatives must be actively considered and weighed against the need for detention.
• Hanningfield v Chief Constable of Essex Police EWHC 243 (QB): Lord Hanningfield was arrested at his home concerning allegations of credit card expenses fraud.20 The High Court found that, while the arresting officer subjectively believed the arrest was necessary, this belief was not objectively reasonable.20 The court considered several factors: Lord Hanningfield had been aware of the police interest for three months without incident; he had previously cooperated with police, attending a voluntary interview for related matters; his age (71) and health conditions; and the absence of any specific, objective grounds to believe he posed a real risk of destroying evidence or interfering with witnesses beyond a “theoretical possibility”.20 The court concluded that voluntary attendance was a viable alternative that had not been rationally discounted, and that summary arrest (and the subsequent detention) was not necessary for a “prompt and effective investigation”.20 This case demonstrates that factors like prior cooperation, the absence of concrete risk indicators, and the feasibility of voluntary procedures weigh heavily against a finding of objective necessity for detention aimed at questioning or evidence preservation. Necessity cannot be founded on “fanciful conjectures”.20

The consistent message from the judiciary is that the necessity threshold is substantial. It requires a demonstrable, objective need for detention that cannot reasonably be met through less intrusive means.

The legal requirement for detention under Section 37(3) to be “necessary” implicitly obliges the Custody Officer to consider whether the stated objectives – securing, preserving, or obtaining evidence – can be reasonably achieved without resorting to continued detention. This flows directly from the high threshold set by the word “necessary” and the principles articulated in cases like McCollum and Hanningfield.19 If evidence can be secured immediately (e.g., seizing items found on the person) followed by release, or if questioning can practicably occur via a voluntary interview arranged after release (perhaps facilitated by pre-charge bail conditions), then authorising continued detention under S37(3) may not meet the objective reasonableness standard. The Custody Officer must evaluate these alternatives; a failure to consider or rationally discount less intrusive options undermines the justification for detention.

Furthermore, the assessment of necessity under Section 37(3) is not a one-off decision made solely upon the detainee’s arrival. It is a dynamic requirement that persists throughout the period of authorised detention. PACE Section 34(2) and Code C Paragraph 1.1 stipulate that detention must cease as soon as the grounds for it no longer apply.13 The initial justification for detention under S37(3) (e.g., the need to interview the suspect) might expire once that action is completed, or if it becomes apparent the action cannot be achieved (e.g., the suspect exercises their right to silence, or necessary searches are concluded without yielding relevant evidence). The periodic reviews of detention mandated by PACE Section 40 are designed, in part, to ensure this ongoing assessment of necessity occurs.21 If, at any point, the continued detention ceases to be necessary for the specific purposes outlined in S37(3), the authority to detain lapses, and the person must be released, irrespective of whether the maximum permitted detention period has been reached.

5.4 Table: Key Case Law on the Necessity Test (PACE S24/S37(3))

The following table summarizes key judicial decisions relevant to the interpretation of the “necessity” threshold:

 

Case Name	Relevant Facts	Court’s Finding on Necessity	Key Principles/Factors Considered
Hayes v Chief Constable of Merseyside Police 1 WLR 517	Arrest for assault. Appeal concerning the application of the necessity test under PACE S24(5).	Established the two-stage test (subjective belief and objective reasonableness) for necessity in arrest.	Necessity requires both genuine belief by the officer and objective reasonable grounds for that belief based on known facts.
McCollum & Others v Chief Constable of the PSNI NIQB 17 (‘Bloody Sunday’)	PSNI sought to arrest former soldiers in England/Wales for interview in NI regarding Bloody Sunday investigation.	Arrest (and subsequent detention) held not necessary.	Offer of voluntary attendance negated necessity. Arguments of administrative convenience or minor gains in effectiveness are insufficient. Necessity requires more than desirability. Less intrusive, practicable alternatives must be considered. Impact of significant delay since the event on the “promptness” requirement.19
Hanningfield v Chief Constable of Essex Police EWHC 243 (QB)	Arrest of Lord Hanningfield at home for alleged expenses fraud.	Arrest (and subsequent detention) held not objectively necessary.	Prior cooperation, knowledge of investigation without incident, age/health, lack of specific risk factors (beyond theoretical possibility) weighed against necessity. Voluntary attendance was a viable alternative not rationally discounted. Necessity cannot be based on “fanciful conjectures”. Necessity must relate to “prompt and effective investigation”.20
R (TL) v Chief Constable of Surrey Police EWHC 129 (Admin)	Arrest of a youth following an allegation; challenge based partly on necessity, specifically whether voluntary attendance was practicable.	Emphasised the need to properly consider voluntary attendance as an alternative to arrest for interview, particularly where the suspect is potentially cooperative. (Finding on specific facts varied).	Voluntary attendance must be considered as a practicable alternative; if it is practicable, arrest solely for interview may not be necessary. Officer must assess likelihood of voluntary attendance realistically.

6. Procedural Requirements and Safeguards

The lawful exercise of the power to detain under Section 37(3) is contingent not only on meeting the substantive threshold of necessity but also on strict adherence to prescribed procedural requirements. These procedures act as vital safeguards for the detainee.

6.1 Making a Written Record (PACE S37(4) & S37(5))

When a Custody Officer authorises detention under the exceptional power in Section 37(3), PACE mandates specific recording and notification procedures:

• Written Record: The Custody Officer must, “as soon as is practicable,” make a written record of the grounds upon which the detention is authorised.8 This record must be entered into the individual’s custody record.16
• Presence of Detainee: Section 37(5) requires that this written record normally be made in the presence of the arrested person.8
• Informing the Detainee: At the time the record is made, the Custody Officer must inform the arrested person of the grounds for their continued detention.8 PACE Code C further stipulates that a detainee must be informed of the grounds for detention before any questioning about an offence commences.16
• Exceptions (S37(6)): The requirements for the detainee’s presence and for informing them at the time the record is made do not apply if the person is, at that time:

• Incapable of understanding what is said to them (e.g., due to intoxication, medical condition);
• Violent or likely to become violent;
• In urgent need of medical attention; or
• Asleep (this exception was added later and also applies during detention reviews under S40).8

These recording and notification requirements are fundamental to ensuring transparency and enabling the detainee to understand the justification for their deprivation of liberty.

6.2 Informing the Detainee of Rights

Upon authorisation of detention, the Custody Officer has a comprehensive duty under PACE Code C, Section 3, to ensure the detainee is informed of their legal rights and entitlements.22 This includes, but is not limited to:

• The right to consult privately with a solicitor, free of charge (Section 6).4
• The right to have someone informed of their arrest and whereabouts (Section 5).22
• The right to consult the PACE Codes of Practice.16
• The right to medical assistance when needed (Section 9).4

This information must be conveyed both orally and by providing the detainee with a written Notice of Rights and Entitlements, available in various languages and formats (including easy read and audio versions) to cater for different needs.25 Ensuring the detainee understands these rights is crucial for enabling them to participate effectively in the process and access safeguards against potential abuses of power.

6.3 Detention Reviews (PACE S40)

If detention authorised under Section 37(3) continues, PACE Section 40 mandates periodic reviews of that detention.21

• Reviewing Officer: For a person arrested but not charged, the review must be conducted by an officer of at least the rank of Inspector who has not been directly involved in the investigation.21 (If the person has been charged, the Custody Officer conducts the review 21).
• Frequency: The first review must occur no later than six hours after detention was initially authorised. Subsequent reviews must take place at intervals not exceeding nine hours.21 Reviews can be postponed under specific, limited circumstances (e.g., impracticability, interviewing in progress, officer unavailable), but must be conducted as soon as practicable thereafter.21
• Purpose: The core purpose of the review for an uncharged detainee is to reassess whether the grounds justifying detention still exist.4 The Review Officer effectively reapplies the tests from Section 37(1) to (6), including the crucial necessity test under Section 37(3) if detention continues to be based on that provision.21
• Representations: The detainee (unless asleep or unfit due to condition/behaviour) and any solicitor representing them who is available at the time must be given the opportunity to make representations to the Review Officer before the decision on continued detention is made.21

Detention reviews provide a regular, structured mechanism for re-evaluating the justification for ongoing detention, ensuring that the necessity requirement under Section 37(3) remains satisfied throughout the detention period.

The justification for detention under Section 37(3), grounded in the necessity test, is only one part of ensuring lawfulness. Compliance with the detailed procedural requirements laid down in PACE and its Codes is equally critical. The steps involved – accurately recording the grounds, informing the detainee promptly, ensuring access to rights and legal advice, and conducting timely reviews – are not mere administrative tasks. They constitute integral components of the legal framework designed to safeguard individual liberty.8 A failure to adhere strictly to these procedures, such as neglecting to record the grounds for detention adequately, failing to inform the detainee, or missing a mandatory review, can render an otherwise potentially justifiable detention unlawful. These procedural safeguards ensure transparency, facilitate accountability, allow the detainee to challenge their detention, and ultimately uphold the balance struck by Parliament between effective law enforcement and the protection of fundamental rights within the police station.3

7. Conclusion

7.1 Summary of the Test

The authority for a Custody Officer to detain an arrested person prior to charge, in circumstances where insufficient evidence exists for that charge, is strictly governed by Section 37(3) of the Police and Criminal Evidence Act 1984. This provision permits detention only if the Custody Officer possesses reasonable grounds for believing that such detention is genuinely necessary. The necessity must relate directly to one of two specific purposes: either to secure or preserve evidence connected to the offence for which the person was arrested, or to obtain such evidence by questioning the individual.8

7.2 The High Standard of “Necessity”

The term “necessary” within Section 37(3) establishes a significant legal threshold. It demands more than mere desirability, convenience, or expediency for the investigation.5 As interpreted by the courts, particularly through the lens of the Hayes two-stage test and subsequent case law like McCollum and Hanningfield, necessity requires an objective justification based on the facts known at the time.19 Crucially, this involves a consideration of whether less intrusive, practicable alternatives – such as voluntary attendance for interview or release on bail – could achieve the evidence-related objectives without resorting to continued detention.19 The necessity must be real and demonstrable, not based on speculation or routine assumptions.20

7.3 The Critical Role of the Custody Officer

The Custody Officer occupies a pivotal position in the application of Section 37(3). They are charged with making an independent assessment, distinct from the arresting officer’s decision, as to whether the stringent criteria for continued detention are met.5 This gatekeeping function is essential for upholding the legislative intent of PACE, which seeks to balance the need for effective criminal investigation with the fundamental right to liberty.3 The decision demands a careful, objective evaluation of the specific circumstances against the demanding legal standard of necessity, always treating detention as a measure of last resort.5

7.4 Final Thoughts on Compliance and Scrutiny

Ensuring the lawful and consistent application of Section 37(3) requires more than just understanding the legal test. Given the potential for investigative pressures to influence decision-making 7 and the critical importance of the Custody Officer’s independent role, robust training, clear internal force policies reflecting APP guidance, and effective supervision and quality assurance processes are vital.5 Adherence to both the substantive requirements of the necessity test and the procedural safeguards outlined in PACE and Code C is paramount. Failures in either aspect can lead to unlawful detention, legal challenges, and undermine public confidence in the police custody process.3 The scrutiny applied by courts in cases challenging detention underscores the importance of meticulous compliance at every stage.

Works cited

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3. The Role of the Custody Officer – Professional Bookshop, accessed on May 5, 2025, https://www.pbookshop.com/media/filetype/9/7/1343982020.pdf
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17. Pre-charge bail statutory guidance (accessible) – GOV.UK, accessed on May 5, 2025, https://www.gov.uk/government/publications/pre-charge-bail-statutory-guidance/pre-charge-bail-statutory-guidance-accessible
18. Custody Toolkit – London – Metropolitan Police, accessed on May 5, 2025, https://www.met.police.uk/SysSiteAssets/foi-media/metropolitan-police/disclosure_2022/may_2022/custody-policy-toolkit-detainees-policy.pdf
19. Court in Bloody Sunday case applies “necessity” threshold for lawful …, accessed on May 5, 2025, https://www.wilmerhale.com/en/insights/blogs/wilmerhale-w-i-r-e-uk/court-in-bloody-sunday-case-applies-necessity-threshold-for-lawful-arrest
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