1. (a) That's right. The tort of false imprisonment exists to protect an individual's liberty. It is another instance of trespass to the person. A plaintiff need only prove that another person has unlawfully deprived them of their liberty, either intentionally or negligently, in any circumstances. If a defendant can prove that the imprisonment of the plaintiff was lawful, such as when a police officer detains a suspected criminal on reasonable grounds, there will be no liability for false imprisonment. It is, however, possible for false imprisonment to have occurred even if the plaintiff was unaware of the imprisonment at the time.
In this case, A has used indirect force (locking the shop) to detain B. B's loss of liberty, although brief, is total. Since A is unlikely to justify his act, B will succeed in a claim based on false imprisonment.