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This article was written by Andrew Fraser - Managing Associate - Canberra

Andrew works in the areas of criminal law and traffic law, providing practical advice in all of his clients’ matters. Andrew has, over many years, developed positive working relationships with prosecutors, magistrates and judges. His no-nonsense approach means he has a reputation for putting forward the best case possible for clients. Andrew has won many matters for his clients, including...

What is a Reasonable Cause? (ACT)


A recent judgment from Justice Loukas-Karlsson in the ACT Supreme Court deals with the need for police to have reasonable cause to interfere with a person’s liberty. A citizen’s liberty is exceedingly important, not just for the individual citizen, but for our whole community. No-one should be held in custody or detained unless all the procedures have been complied with and their rights respected. In the ACT those rights are enshrined in a Human Rights Act 2004, which has as its primary source the International Covenant on Civil and Political Rights. 

The 2021 decision of Tran v Stapleton overturned the conviction of a Canberra woman on a drug-driving charge because she was wrongfully detained by police. Among other things, the court ruled that the sighting of a car outside a house associated with drug use was not “reasonable cause” to stop the vehicle and submit the driver to a drug test.   

Tran v Stapleton [2021] ACTSC 1

The defendant in this matter was pulled over by plainclothes police in an unmarked police vehicle. She was originally charged with two counts of drug trafficking and one of drug possession as well as drug driving.

A Magistrate dismissed the first three charges, ruling that an admission and subsequent evidence obtained during a search of the car were inadmissible as evidence because they had been illegally or improperly obtained (s138, Evidence Act).

That ruling, however, did not extend to the evidence in relation to the drug-driving.

The Appeal

The woman contested the police assertion that her manner of driving provided reasonable cause to detain her, and to require her to remain on the roadside for an extended period, to allow a drug test to be carried out.

She contended that the results of that drug test were inadmissible against her as they had been unlawfully or improperly obtained, not only because the police had acted improperly but particularly because they did not have the requisite reasonable cause to stop her in relation to drug driving.  

Factual issues

It was contended for the driver that one of the policemen told her of generic powers that had no direct application to her particular circumstance. This was done to obtain her consent for a search of her vehicle and the policeman’s actions had tainted the validity of that consent. Further, she was not cautioned before questioning.

Material inconsistencies between the two policemen’s evidence were raised: one said the car was in one lane, one said it was in the other; one said the car was veering and crossing lanes toward the median strip, the other only that it was not always “strictly within its lane”.  

The police tried to contend that they had been merely conducting a traffic stop, but they had not asked the woman about her manner of driving, a normal part of a traffic stop for drug-driving.

Justice Loukas-Karlsson found that the Magistrate’s rejection of the woman’s evidence was “contrary to compelling inferences”.

“It is appropriate for the police officers’ evidence in relation to the manner of driving to be assessed in the context of both the material inconsistencies and in the context of other adverse conduct, on the day in question and otherwise …” Her Honour found. “I do not accept, having considered all the evidence, in light of the authorities [previous judgments] discussed … that the car driven by the appellant was driven in the manner given in evidence by the police officers.”

What are reasonable grounds?

The High Court case of George v Rockett ((1990) 170 CLR 104) was drawn on considerably in Justice Loukas-Karlsson’s judgment. That case held that “reasonable grounds” requires “the existence of facts which are sufficient to induce that state of mind in a reasonable person”.

The view must be formed by the arresting officer, and not on the “bald assertion” of another police officer. Such accountability was “the compromise between the values of individual liberty and public order”.

Whether a person had reasonable grounds for forming a suspicion or a belief is to be determined not according to their subjective beliefs at the time but according to an objective criterion.

Arguments made by the defence on appeal

The Appellant submitted that police did not have reasonable cause to suspect that she had, at the relevant time, a drug in her system. Therefore, it was submitted that the direction for her to remain on the road side for 30 minutes was a form of unlawful detention and, as a consequence, the oral fluid analysis was taken illegally and should be excluded from evidence.

In support of this, a number of inconsistencies in police evidence were noted, including particularly that one policeman said that the other one had told him that the lady’s car had been parked “at an address … that was known by police to be associated with drug activity”. However, under cross-examination, that other policeman said there had been no reference to such an address and he “expressed no knowledge of any connection between the car and the …. address”.

Arguments made by the prosecution

In written submissions, the prosecution submitted that a combination of circumstances – observing the car leaving a known drug-associated property and the manner of driving – were considerations that “rationally could bear upon the issue of whether a person may be driving with a drug in their system”.

Potential breaches of the Human Rights Act

The Judge said, “I do not accept that the car driven by the Appellant was driven in the manner given in evidence by the police officers. In my view, [the arresting officer] did not have reasonable cause to suspect that the Appellant had a drug in her body.”

The Judge noted especially the provision of the Evidence Act (s138(3)(f)), which demands consideration of whether the impropriety of what police did was contrary to or inconsistent with a right of a person recognised by the International Covenant on Civil and Political Rights.

She quoted Article 9.1 of the Covenant which says, “Everyone has the right to liberty and security of person. No one shall be subjected to arbitrary arrest or detention. No one shall be deprived of his liberty except on such grounds and in accordance with such procedure as are established by law.”

Her Honour declared that the contravention in the instant case “raises potential breaches” of the ACT’s Human Rights Act, specifically s13, which deals with freedom of movement, and s18, which concentrates on the right to liberty and security of person.

The final words were: “The appeal is upheld on all grounds. The finding of guilt is overturned. Noting that, in the absence of the roadside drug screening test results and oral fluid analysis, the Prosecution has no evidence to offer on the charge, the charge is dismissed.”

If you require legal advice or representation in any legal matter please contact Armstrong Legal. 

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