In UK legislation, what does &quot;reasonable grounds to suspect&quot; mean?
<p>In the Customs and Excise Management Act of 1979, <a href="http://www.legislation.gov.uk/ukpga/1979/2/section/161" rel="nofollow noreferrer">section 161</a> the language "if there are reasonable grounds to suspect" appears. Practically, where is the line drawn for "reasonable," and how stringent is "suspect"? </p>

<p>I'm essentially trying to figure out how this compares to "Probable Cause" under the US 4th Amendment. </p>

<p>The concept of <strong>reasonable suspicion</strong> is used throughout the common law world. While the <a href="https://en.wikipedia.org/wiki/Reasonable_suspicion" rel="nofollow noreferrer">Wikipedia article</a> (at present) focuses on the term as used in the ‘stop and search’ context of <em><a href="https://en.wikipedia.org/wiki/Terry_v._Ohio" rel="nofollow noreferrer">Terry v. Ohio</a></em>, a different line of authority has emerged in the interpretation of police powers (both with and without warrant) in Commonwealth countries.</p>

<h2>Commonwealth case law</h2>

<p>One significant authority is <em>Hussien v Chong Fook Kam</em> <a href="http://www.bailii.org/uk/cases/UKPC/1969/1969_26.html" rel="nofollow noreferrer">[1970] AC 942</a>, a decision of the <a href="https://en.wikipedia.org/wiki/Judicial_Committee_of_the_Privy_Council" rel="nofollow noreferrer">Privy Council</a> on appeal from the Federal Court of Malaysia. This case concerned the interpretation of a power of arrest, under the Malaysian <em>Criminal Code</em>, which arose if “reasonable suspicion existed of [the plaintiffs’] having been concerned in an offence …”</p>

<p><a href="https://en.wikipedia.org/wiki/Patrick_Devlin,_Baron_Devlin" rel="nofollow noreferrer">Lord Devlin</a>, delivering the judgment of the court, said:</p>

<blockquote>
  <p>Suspicion in its ordinary meaning is a state of conjecture or surmise
  where proof is lacking: “I suspect but I cannot prove.” <strong>Suspicion arises
  at or near the starting-point of an investigation of which the obtaining of
  prima facie proof is the end.</strong> When such proof has been obtained, the
  police case is complete; it is ready for trial and passes on to its next
  stage. It is indeed desirable as a general rule that an arrest should not
  be made until the case is complete. But if arrest before that were forbidden, it could seriously hamper the police.</p>
  
  <p>To give power to arrest on reasonable suspicion does not mean that it is always or even ordinarily to be exercised. It means that there is an <strong>executive discretion</strong>. In the exercise of it many factors have to be considered besides the strength of the case ... There is no serious danger in a large measure of executive discretion in the first instance because in countries where common law principles prevail the discretion is subject indirectly to judicial control.</p>
</blockquote>

<p>Lord Devlin noted that “the test of reasonable suspicion prescribed by the Code is one that has existed in the common law for many years,” and continued, citing <em>Dumbell v Roberts</em> [1944] 1&nbsp;All&nbsp;ER&nbsp;326:</p>

<blockquote>
  <p>The police are not called upon before acting to have anything like a prima facie case for conviction ... <strong>Prima facie proof consists of admissible evidence. Suspicion can take into account matters that could not be put in evidence at all.</strong></p>
</blockquote>

<p>The Privy Council’s judgment was quoted with approval by the High Court of Australia in <em>George v Rockett</em> <a href="https://www.austlii.edu.au/au/cases/cth/HCA/1990/26.html" rel="nofollow noreferrer">(1990) 170 CLR 104</a>.</p>

<h2><em>Terry v. Ohio</em></h2>

<p><em>Terry v. Ohio</em>, <a href="https://supreme.justia.com/cases/federal/us/392/1" rel="nofollow noreferrer">392 U.S. 1</a> (1968) involved testing police conduct “by the <a href="https://en.wikipedia.org/wiki/Fourth_Amendment_to_the_United_States_Constitution" rel="nofollow noreferrer">Fourth Amendment’s</a> general proscription against unreasonable searches and seizures,” and deciding whether, if the petitioner’s constitutional right had been violated, the <a href="https://en.wikipedia.org/wiki/Exclusionary_rule" rel="nofollow noreferrer">exclusionary rule</a> should prevent the use of evidence obtained in the search. The Supreme Court held:</p>

<blockquote>
  <p>[T]he quite narrow question posed by the facts before us [is] whether it is always unreasonable for a policeman to seize a person and subject him to <strong>a limited search for weapons</strong> unless there is probable cause for an arrest.</p>
</blockquote>

<p>It is important to remember the constitutional context of <em>Terry v. Ohio</em>. The analysis of a statutory grant of search powers upon reasonable suspicion, particularly in a jurisdiction with no constitutional bill of rights, is a different exercise. It is also significant that one purpose of the Fourth Amendment was to curtail the abuse of the royal <a href="https://en.wikipedia.org/wiki/Writ_of_assistance" rel="nofollow noreferrer">writ of assistance</a>, which a customs officer must hold to exercise the power conferred by s&nbsp;161 of the <em>Customs and Excise Management Act</em>!</p>

<h2>The <em>Customs and Excise Management Act</em></h2>

<p>There is a good chance that a statute of the United Kingdom, conferring police-like powers on a public officer upon reasonable suspicion, would be interpreted in accordance with the long history of the use of that term at common law. The scope of any litigation would probably depend on the procedure that brought the question before the court – for example, judicial review of a warrant, an action to recover goods, or an action for damages.</p>

<p>I am not aware of any case law on s&nbsp;161. Perhaps there are not that many customs officers holding a royal writ of assistance. But any court reviewing the scope of that power would consider the purpose of the legislation, as well as the traditional common law meaning of ‘reasonable suspicion.’</p>

<p>When the legislature uses the word “reasonable” they are instructing the court to apply the <a href="https://en.m.wikipedia.org/wiki/Reasonable_person" rel="nofollow noreferrer">reasonable person</a> test. </p>

<p>For this law, the”reasonable person” is a trained customs officer, neither a novice nor an expert, neither paranoid nor overly trusting. The question to be answered is if this hypothetical person  would have “grounds to suspect” in the particular circumstances.</p>

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