1. False imprisonment is the act of unlawfully restricting the physical freedom of another. Actual incarceration is not essential; there must have been complete restriction of the plaintiff's liberty of action by the defendant.

2. Details
a) A false arrest will suffice even if it is made merely under threats or persuasion, or deception, without physical force, for the movements of the person will then be under control of the tortfeasor.
Harnett v. Bond 1925 - lunatic was falsely told to stay at the institution.
b) The control must have been complete, not partial: prevention from passing along a certain path or entering a certain place is not enough (though this may be a nuisance):
Bird v. Jones 1845 - visitor area restricted by the police during a specacle.
Also: Robinson v. Balmain Ferry 1910 (Privy Council) - man wanted to leave the ferry.
c) Only active imposition of a restraint will make up the tort, unless there is a special duty to act:
Herd v. Weardale Coal Co. 1915 - a minor taking his shift wanted to leave the mine before the shift ended.
d) The tort can only be committed intentionally: Sayers v. Harlow 1958 - woman accidently locked in a toilet.
e) The defendant does not have to be aware: Meering v. Graham White Aviation 1919 - employee held by his employer who thought him a thief; he got extra damages because he knew he was being kept. Historically, this was different: Herring v. Boyle 1834 - headmaster kept pupil, this the latter did not know - back then this was no tort. The House of Lords upheld the Meering decision in Murray v. Ministry of Defense 1988.
f) Customers not having paid is no defence for locking them up: Sunbolf v. Alford 1838
g) If one has the chance to escape he has to do that, even if this means committing trespass to land:
Wright v. Wilson 1699

3. In addition to (or, better, in the first place) the action in tort everyone who is imprisoned, otherwise than by the due process of the law, will have the right to be immediately released by means of the writ of habeas corpus.

4. It is possible to imprison a person without committing an assault, as where one person locks another in a room.