A claimant can establish false imprisonment if they can show that:
- The defendant detained them; and
- That detention was unlawful: Bird v Jones (1845) 115 ER 668.
There is no need to establish that the claimant suffered any loss: R (Lumba) v Secretary of State for the Home Department  1 AC 245. However, the absence of any loss may affect the damages awarded.
This means that the fact that the claimant could have been lawfully detained in the circumstances (and so suffered no loss) is irrelevant.
Detention is any act compelling the claimant to remain in a particular location against his will: Bird v Jones (1845) 115 ER 668. There is no need for the claimant to be touched physically by the defendant. Examples including locking the room the claimant is in or stationing people to block the claimant’s way out.
There must be an ‘act’ of detention. An omission, such as the failure to unlock a door which was lawfully locked, is not a detention: Iqbal v Prison Officers Association  QB 732.
The act must completely prevent the claimant from leaving the area. Merely stopping the claimant from using a particular route, leaving them free to leave any other way, is not detention: Bird v Jones (1845) 115 ER 668. This is so even if the other routes are less convenient. There must be total obstruction.
If there is total obstruction, it does not matter that it was only for a short period of time: Walker v Commissioner of Police of the Metropolis  1 WLR 312.
The Claimant’s Knowledge of Detention
It is unclear whether it is relevant that the claimant was unaware that they were being imprisoned.
The House of Lords in R v Bournewood Mental Health Trust (ex parte L)  1 AC 458 held that a mental patient was not detained in an unlocked hospital because he was unaware of the fact that if he tried to leave he would be prevented from doing so. However, this decision has been replaced in the context of mental health hospitals with the statutory detention regime under the Mental Capacity Act 2005.
The idea that the claimant’s knowledge is irrelevant was disapproved of by Lord Griffiths in Murray v Ministry of Defence  1 WLR 692 and Atkin LJ in Meering v Grahame-White Aviation (1919) 122 LT 44. While these remarks were obiter they have received recent (also obiter) approval by the Supreme Court in R (Lumba) v Secretary of State for the Home Department  1 AC 245.
It is likely that future courts will follow the views of the Supreme Court in Lumba. This means that it is probably not relevant that the claimant did not know they were unable to leave.
The Defendant’s State of Mind
The defendant must intend, or subjectively foresee the possibility of, imprisonment: Iqbal v Prison Officers Association  QB 732 (Smith LJ). This means that if the defendant locks a room thinking it is empty, they are not unlawfully detaining a claimant who happens to be inside.
If the defendant is objectively negligent in imprisoning the claimant, the claimant should sue for negligence instead. Loss of liberty is a recoverable head of loss in the tort of negligence: W v Home Office  Imm AR 302.
Detention Via Intermediaries
The defendant’s actions must be directly responsible for the detention. If the defendant directs a third-party to enact the detention, the defendant is only liable if:
- The third-party acted as their agent; or
- The third-party did not exercise independent judgement and discretion: Davidson v Chief Constable of North Wales  2 All ER 597.
It is not unlawful to make the claimant’s exit from a place he voluntarily entered conditional on a reasonable and fair action: Robertson v Balmain New Ferry Company (1906) 4 CLR 379. For example, making the claimant pay a small fee to leave may not be unlawful.
Police and other State authorities have statutory powers to make lawful arrests and detention. See particularly the Police and Criminal Evidence Act 1984.
Not all breaches of statutory conditions render the detention unlawful, however. Any illegality must take the officer’s acts completely outside of the ambit of their lawful powers for the detention to be considered unlawful, and the officer probably must be aware of this (acting in bad faith): Hague v Deputy Governor of Parkhurst Prison  1 AC 58.
If a valid order for detention is withdrawn, there is no longer lawful authority to detain and subsequent detention is unlawful: R v Governer of Brockhill Prison ex parte Evans  2 AC 19.
If the conditions of the detention are unlawful, the claimant’s cause of action lies in other torts, such as negligence: Hague v Deputy Governor of Parkhurst Prison  1 AC 58.