The following should be a simple question from an RFS volunteer, but it requires quite a long answer. The question:
… relates to a witness to a motor vehicle accident .
The scenario is: You are driving along a road (say in NSW, my home State) and witness a fairly serious motor vehicle accident. You stop and render what assistance you can i.e. give first aid, calling police and ambulance, trying to protect the incident from other traffic. The police arrive and start to do their usual thing of managing traffic, examining the accident scene, breath testing and interviewing the driver(s) of the vehicle(s) involved in the accident, and interviewing witnesses. You approach the police person and advise him/her that you were a witness but have an important appointment elsewhere so cannot stay any longer. You offer the police person a business card or piece of paper with your name and contact details.
My question: Can you, not having been involved in the accident only a witness, leave the scene when you wish or can the police direct you to remain at the scene until they get around to interviewing you?
The short answer is that you can leave the scene when you wish and no, the police cannot direct you to remain at the scene until they get around to interviewing you. The long answer is more complex.
Arrest
An arrest occurs when police make it clear that a person is no longer free to go about their business (R v O’Donoghue (1988) 34 A Crim R 397, 401). Although it is usual to indicate an arrest by touching the person and saying ‘you’re under arrest’, there is in law ‘… no magic formula; only the obligation to make it plain to the suspect by what is said and done that he is no longer a free man’ (R v Inwood [1973] 2 All ER 645, 649; see also Alderson v Booth [1969] 2 QB 216, 220).
If the police ‘direct you to remain at the scene’ then they are communicating to you that you are no longer free to go about your business and that is an arrest.
Purpose of arrest
‘At common law, the only legitimate purpose of an arrest was to bring a person before a court to answer an allegation of wrongdoing. It was impermissible to arrest a person simply to allow police to ask questions (Bales v Parmeter (1935) 35 SR (NSW) 182) or for the purpose of investigating that person’s possible involvement in a criminal offence.’ (see Michael Eburn, Rod Howie and Paul Sattler, Hayes and Eburn Criminal Law and Procedure in NSW (2013, 4th ed, Lexis/Nexis), [11.46]; Williams v R (1986) 161 CLR 278 and Law Enforcement (Powers and Responsibilities) Act 2002 (NSW) s 99).
In Collins v Wilcock [1984] 3 All ER 374 two police officers observed a women who they suspected of ‘soliciting for the purpose of prostitution’. The officers asked the woman to get into the car so they could ask her questions, which she refused to do and walked away. A police officer got out of the car and followed her order to question her. Again the woman refused to speak to the police and continued to walk away. The police officer then took hold of her arm in order to stop her. The woman swore at the officer and scratched the officer’s arm. She was convicted of assaulting a police officer in the execution of her duty. On appeal the conviction was set aside. Robert Goff LJ said:
A police officer has no power to require a man to answer him, though he has the advantage of authority, enhanced as it is by the uniform which the state provides and requires him to wear, in seeking a response to his inquiry. What is not permitted, however, is the unlawful use of force or the unlawful threat (actual or implicit) to use force and, excepting the lawful exercise of his power of arrest, the lawfulness of a police officer’s conduct is judged by the same criteria as are applied to the conduct of any ordinary citizen of this country.
Arrest to establish identity
There are some circumstances where a police officer can detain a person in order to establish their identity. The Law Enforcement (Powers and Responsibilities) Act 2002 (NSW) s 11 says:
A police officer may request a person whose identity is unknown to the officer to disclose his or her identity if the officer suspects on reasonable grounds that the person may be able to assist in the investigation of an alleged indictable offence because the person was at or near the place where the alleged indictable offence occurred, whether before, when, or soon after it occurred.
The police may also require proof of identity (s 19). Failure to comply is an offence (s 12) and so could justify an arrest (s 99) and the use of force to ensure compliance (ss 230 and 231).
Application
Applying those principles to the given scenario, requiring a person to remain at the scene until police get around to interviewing them would be an arrest. Because the purpose of the arrest is to ask questions, not to bring the person before the court to face an allegation of wrongdoing, it would be an unlawful arrest. Section 11 of the Law Enforcement (Powers and Responsibilities) Act 2002 (NSW) does not allow detention to ask questions and would not be relevant in the given scenario as my correspondent was volunteering proof of their identity so the police could locate them later in order to complete their investigation.
This brings us full circle back to the short answer: you can leave the scene when you wish and no, the police cannot direct you to remain at the scene until they get around to interviewing you.
Australian Emergency Law 
Hi Michael. Very interesting post.
I was wondering how much the answer changes if the person were involved in the accident, either as a driver or passenger. I understand it to be illegal for a person involved in an accident to leave the scene until police/emergency services arrives. Once they have, however, and anyone injured has been seen to by paramedics, can one freely leave? Assuming of course that the police aren’t arresting them for dangerous driving or drink driving or such.
Thanks.
Fundamentally the answer is no different if the person was the driver of a vehicle involved in the collision.
A driver is guilty of an offence if he or she knows or ought to know that the vehicle they are driving has been involved in an accident where someone has been injured and the driver ‘fails to stop and give any assistance that may be necessary and that it is in the person’s power to give’ (Road Transport Act 2013 (NSW) s 146). A driver who is ‘involved’ in a crash must give the ‘required particulars’ (that is their name and address. the name and address of the owner of the vehicle, the vehicle’s registration number and ‘an explanation of the circumstances of the crash) to a police officer if anyone is killed or injured, if they have not given their particulars to the other driver’s involved (eg if the other driver was transported to hospital), if other driver’s did not exchange their details, if any vehicle was towed from the scene or if requested to do so. Those details must be given as soon as possible and in any event within 24 hours (Road Rules 2014 (NSW) rule 287). A police officer may arrest a person involved in a fatal accident in order to require them to undergo blood and urine tests (Road Transport Act 2013 (NSW) Schedule 3, cl 12). Failure to do all those things may constitute an offence for which the driver can be arrested. One has to submit to a breath test but there would have to be a question of how long you have to wait, imagine if police pulled you over for a random breath test but then said ‘wait there ’till I get to you in an hour’ – I don’t think it would be an offence to refuse to wait that long, so be it at the scene of the accident, where you could say ‘I’m willing to submit to a breath test, but in a reasonable time not when it suits you’.
So in answer to the question, if the people have been assisted and the police are not arresting the person from dangerous driving or drink driving then the person is free to go. But if the police did say ‘we require you to wait to undergo a breath test’ or ‘you need to tell us what happened’ then you’re at that point where your either under arrest or you are not. That is where the prudent person says ‘I’ll wait’ and the courageous person says ‘am I under arrest? Because if I’m not then I’m going’ That may just prompt the officer to say ‘yes you are under arrest’. Whether that would be a lawful arrest or not would depend on many factors, for example if you may be willing to give the prescribed particulars but say ‘You need to talk to me, now, rather than that other person as I’m more important than they are’. In that case your not refusing to give the particulars and it does say you’ve got 24 hours so you may be able to say ‘I committed no offence’ but the reality is that its the police that can put you in the caged truck, take you to the cells, charge you with the offence, and then wait whilst a court takes a year and a lot of your money to decide whether or not you’ve committed the offence.
The short answer is ‘if you are not under arrest, you’re free to go’; the sensible answer is if you have been involved in an accident that is serious enough for the police to attend and the police ask you to wait until they get to you, you do so.