Principle of legality
10.23 The principle of legality provides some protection to the principle of mens rea. When interpreting a statute, courts will presume that Parliament did not intend to create a strict liability offence, unless this intention was made unambiguously clear.
10.24 In CTM v The Queen, for example, the High Court considered whether the common law defence of honest and reasonable mistake of fact applies to s 66C(3) of the Crimes Act 1900 (NSW) (Crimes Act), which makes it an offence for a person to have sexual intercourse with another person between the ages of 10 and 16. The majority of the High Court stated:
While the strength of the consideration may vary according to the subject matter of the legislation, when an offence created by Parliament carries serious penal consequences, the courts look to Parliament to spell out in clear terms any intention to make a person criminally responsible for conduct which is based on an honest and reasonable mistake.
10.25 An amendment to the Crimes Act in 2003 had removed the express statutory defence under s 77(2)(c) that the person ‘had reasonable cause to believe, and did in fact believe, that the child was of or above the age of 16 years’. It was designed to provide equal treatment of sexual offences against males and females.
10.26 A majority of the High Court held that the offence in s 66C was not an absolute liability offence, despite the repeal of s 77(2), because it did not prevent the ongoing operation of the common law principle that an honest and reasonable mistake generally precludes criminal liability. The Court stated:
the New South Wales Parliament regarded the ‘express defence’ in s 77(2) as no longer appropriate. It was a defence that, in its terms, differentiated between homosexual and heterosexual activity, so it at least had to be changed if there were to be the desired equalisation. It could not have been left as it was. Yet the problem to which that provision was addressed did not disappear; and the long-standing and well-understood principle which provided an alternative response to the same problem remained potentially applicable in the absence of ‘the clearest and most indisputable evidence [concerning] the meaning of the Act’.
10.27 The imposition of strict or absolute liability is seen to engage and limit the presumption of innocence protected under art 14.2 of the International Covenant on Civil and Political Rights (ICCPR),  because it allows for the imposition of criminal liability without proof of fault. Article 14.2 therefore provides some protection to the principle of mens rea. While international instruments cannot be used to ‘override clear and valid provisions of Australian national law’, where a statute is ambiguous, courts will generally favour a construction that accords with Australia’s international obligations.
This section and the section following refer to mens rea rather than fault elements, as it relates to the protection of the underlying common law principle, rather than the statutory expression of the principle under the Criminal Code.
However, where an offence in a Commonwealth law encroaches upon a constitutional right (express or implied), imposing strict or absolute liability on the offence may mean it is more difficult to establish that the offence is a proportionate limitation on the constitutional right.
The principle of statutory interpretation now known as the ‘principle of legality’ is discussed more generally in Ch 2.
He Kaw Teh v The Queen (1985) 157 CLR 523, 528 (Gibbs CJ); Sherras v De Rutzen  1 QB 918.
CTM v The Queen (2008) 236 CLR 440,  (Gleeson CJ, Gummow, Crennan and Kiefel JJ). This finding was supported by the other judges: Ibid ,  (Kirby J),  (Hayne J), – (Heydon J).
New South Wales, Parliamentary Debates, Legislative Assembly, 7 May 2003, 376 (Bob Debus, Attorney–General).
New South Wales, Parliamentary Debates, Legislative Assembly, 21 May 2003, 834 (Kristina Keneally).
CTM v The Queen (2008) 236 CLR 440,  (Gleeson CJ, Gummow, Crennan and Kiefel JJ).
International Covenant on Civil and Political Rights, opened for signature 16 December 1966, 999 UNTS 171 (entered into force 23 March 1976).
Minister for Immigration v B (2004) 219 CLR 365,  (Kirby J).
Minister for Immigration and Ethnic Affairs v Teoh (1995) 183 CLR 273, 287 (Mason CJ and Deane J). The relevance of international law is discussed more generally in Ch 2.