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 offences were of strict liability:

1. Other sections of the Act provided a defence of due diligence, but this section did not.
2. The offence was plainly not truly criminal in character.
3. The legislation dealt with an issue of social concern, namely, gambling among young people.

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.