The House of Lords held it was not necessary to displace the presumption of mens rea, nor was it ‘compellingly clear’ that Parliament intended liability to be strict. The mens rea was lack of an honest belief that the complainant was aged 14 or over.

The defendants were involved in the construction of a building in Hong Kong. The building collapsed and they were charged with having deviated in a material way from the plans. There was no evidence that they realized the deviation they made was material.

The Privy Council laid out the test for judges to use when determining whether an offence imposes strict liability. First, there is a presumption of law that mens rea is required before a person can be held guilty of a criminal offence and that presumption is particularly strong where the offence is ‘truly criminal’ in character. The presumption can be displaced only if this is clearly or by necessary implication the effect of the statute and only where the offence is concerned with an issue of social concern. However, even where a statute is concerned with such an issue, the presumption of mens rea stands unless it can also be shown that the creation of strict liability will be effective to promote the object of the statute by encouraging greater vigilance to prevent the commission of the prohibited act.

The Ds were newsagents. One of their employees sold a lottery ticket to a boy aged 13½. The Ds were charged with offences relating to selling lottery tickets to persons under 16.

The offences were of strict liability:

D had been convicted of managing premises where cannabis was used. D was a teacher. She sublet a house to students. She did not know the students had been smoking cannabis.

Her appeal was allowed by the House of Lords. If a section is silent as to mens rea, there is a presumption that, in order to give effect to the will of Parliament, judges must read in words appropriate to require mens rea.