Principle of legality

In Coco v The Queen [1994] HCA 15; (1994) 179 CLR 427 at 437., Mason CJ, Brennan, Gaudron and McHugh JJ said:
"The insistence on express authorization of an abrogation or curtailment of a fundamental right, freedom or immunity must be understood as a requirement for some manifestation or indication that the legislature has not only directed its attention to the question of the abrogation or curtailment of such basic rights, freedoms or immunities but has also determined upon abrogation or curtailment of them. The courts should not impute to the legislature an intention to interfere with fundamental rights. Such an intention must be clearly manifested by unmistakable and unambiguous language. General words will rarely be sufficient for that purpose if they do not specifically deal with the question because, in the context in which they appear, they will often be ambiguous on the aspect of interference with fundamental rights."
The joint judgment in Coco went on to identify as the rationale for the presumption against modification or abrogation of fundamental rights an assumption that it is highly improbable that Parliament would "overthrow fundamental principles, infringe rights, or depart from the general system of law" without expressing its intention with "irresistible clearness"[16]. In R v Home Secretary; Ex parte Pierson [1997] UKHL 37; [1998] AC 539 at 587, 589., Lord Steyn described the presumption as an aspect of the principle of legality which governs the relations between Parliament, the executive and the courts. The presumption is not merely a common sense guide to what a Parliament in a liberal democracy is likely to have intended; it is a working hypothesis, the existence of which is known both to Parliament and the courts, upon which statutory language will be interpreted. The hypothesis is an aspect of the rule of law.

The principle of legality "governs the relations between Parliament, the executive and the courts."[329] It is an aspect of the rule of law. The presumption to which it gives rise, that it is highly improbable that Parliament would act to depart from fundamental rights or principles without expressing itself with "irresistible clearness"[330], has been described as a working hypothesis, known to both the Parliament and the courts, upon which statutory language will be interpreted[331]. It would appear to accord with that principle and hypothesis that the fundamental right, freedom, immunity or other legal rule which is said to be the subject of the principle's protection, is one which is recognised by the courts and clearly so.