One of the rights that individuals hold most dear is that of liberty, and deprivation of the right should not occur unless it is justified. Therefore, if a person is under arrest, there are a number of important requirements that must be met in order for an action of arrest to be considered lawful.
There must be a sufficient act of arrest
First, there should be a number of physical and verbal actions or statements that an arrestor must make, which can entail the physical restraining of a person, or communicating to the person that they no longer have the freedom to go about as they please (e.g. “you are under arrest) , while also making some physical contact with the suspect. In terms of verbally communicating to the suspect, there is no need to use specific words but rather, if it is clearly communicated to the person that they are under arrest, such an action may be considered sufficient.
If it is a police officer who informs a person that they are under arrest, and the officer simply touches the person, even if the person does not submit to the action, the arrest will still be considered valid. As a consequence, if the person escapes or makes an attempt to escape, they may be committing an offence of attempting to escape from custody or resist arrest.
It isn’t necessary for a person who is arrested to be confined to a specific area. However, it should be communicated to the person that they must remain in the presence of the arrestor.
The person must understand that they are under arrest
One of the important aspects of the act of arresting an individual is that the action must be unequivocal. In the event that the person accompanies a police officer believing they were merely accompanying the officer, rather than knowing they have been arrested; in such a scenario, this may not be considered a valid arrest. Although it should be highlighted that determining whether the person is volunteering to accompany an officer or under arrest can sometimes be difficult, as was the case in R v Inwood  1 WLR 647;  2 AII ER 645, where Inwood attended a police station voluntarily to answer questions regarding a theft. At the conclusion of the questioning, an officer informed Inwood that he would be charged with theft, and began to take his fingerprints without informing him that he was being placed under arrest. Subsequently, Inwood attempted to leave the police station and assaulted a number of officers in the process.
On appeal against his conviction, the issue that was considered was whether there was a lawful arrest prior to Inwood’s attempts to leave the police station. The Court of Appeal held that it was not clearly communicated to Inwood that he was under arrest, and observed that the question of whether a person has been arrested is a question of fact (at 649):
“It all depends on the circumstances of any particular case whether in fact it has been shown that a man has been arrested, and the court considers it unwise to say that there should be any particular formula followed. No formula will suit every case and it may well be that different procedures might have to be followed with different persons depending on their age, ethnic origin, knowledge of English, intellectual qualities, physical or mental disabilities. There is 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.”
The person must be informed of the reason for their arrest
It probably goes without saying – but we’ll say it anyway – the person must be told why they are under arrest, such as the offence they have been suspected of committing, or the factual basis behind their arrest, as outlined in s 3ZD of the Crimes Act 1914 (Cth) for example, which states the following:
“(1) A person who arrests another person for an offence must inform the other person, at the time of the arrest, of the offence for which the other person is being arrested.
(2) It is sufficient if the other person is informed of the substance of the offence, and it is not necessary that this be done in language of a precise or technical nature.
(3) Subsection (1) does not apply to the arrest of the other person if:
(a) the other person should, in the circumstances, know the substance of the offence for which he or she is being arrested; or
(b) the other person's actions make it impracticable for the person making the arrest to inform the other person of the offence for which he or she is being arrested.”
In addition to being informed of a reason as to why a person is being placed under arrest, the reason behind the action must also not be vague, uncertain or ambiguous.
Reasonable force may be used when placing a person under arrest
In the course of arresting a person, the force used must be proportionate taking into account the surrounding circumstance of the situation (per Slaveski v Victoria  VSC 441).