A legal process seeking a judicial determination of the legality of a person’s detention, and otherwise to secure their release. Historically such a process was commenced by a writ of habeas corpus ad subjiciendum, directed to the custodian responsible for the person’s detention, requiring them to produce the person or bring them before the court. The Latin words mean, in essence, “bring forth the body” or more literally, “that you have the body to submit”.

The writ of habeas corpus was described in the eighteenth century by William Blackstone as a “great and efficacious writ in all manner of illegal confinement”: Commentaries on the Laws of England (1765–1769), vol 3. 

In Phillip v Director of Public Prosecutions [1992] 1 AC 545, 558 (PC), Lord Ackner said:

“Where a person alleges that his detention or imprisonment is unlawful the classic remedy is to apply for a writ of habeas corpus ad subjiciendum. By its terms the High Court commands the production of the aggrieved subject and inquires into the cause of his imprisonment or detention. If there is no legal justification for the detention, the detained party is ordered to be released. The very basis of the writ is the allegation and the prima facie evidence in support of it, that the person to whom the writ is directed is unlawfully detaining another in custody: Barnado v. Ford [1892] A.C. 326, 339, per Lord Herschell.”

In R v Secretary of State for the Home Department, Ex p Khawaja [1984] AC 74, 111 (HL(E)), Lord Scarman said:

“Every person within the jurisdiction enjoys the equal protection of our laws. There is no distinction between British nationals and others. He who is subject to English law is entitled to its protection. This principle has been in the law at least since Lord Mansfield freed ‘the black’ in Sommersett’s Case (1772) 20 St.Tr. 1.”