The origin of requiring a written warrant from a magistrate or judge, reviewed and signed in advance, and typically accompanied by a sworn oath from the investigator as to the facts of the case, dates back to 1215 with the inclusion of a warrant clause in Britain’s Magna Carta. Throughout the democratic world, the court order or warrant is now a legal precondition for use of most intrusive police power or surveillance.
Then, as now, the intent of a warrant, secured before any search of premises (or seizure of goods or personal papers) occurred, was to prevent arbitrary or abusive use of authority. Given the concept of a professional police force would not develop until six centuries later (articulated by Sir Robert Peel in the early 1800s), the warrant requirement became a foundational check in common law countries, preventing local sheriffs, deputies, reeves and wardens from overstepping their authority and maliciously tormenting individuals, households or communities with whom they had some grievance.
That is accomplished by having officers apply in writing to an impartial court official or government supervisor, in advance and with a sworn deposition of the facts, prior to them conducting the search, which they were only permitted to commence once they had a signed, notarized warrant in hand. Needless to say, this documentary step in due process does not eliminate entirely potential for overreach or abuse. Revolutionaries in British and American colonies were targeted by ‘general warrants’ in the eighteenth centuries, and all manner of businesses chaffed against ‘writs of assistance’ which were warrants meant to compel their collaboration with investigations of the Crown.
Sources: J.F. Shattack, Rights of Privacy (Toronto, 1977), pp. 3-4; J. Fontana and D. Keeshan, The Law of Search and Seizure in Canada (2017), p. 55.