The rule that ignorance of the law excuses no one has been used by the courts throughout the years and applied the same in criminal law. It presupposes that every person knows the law. This general principle admits some exceptions for there are situations that ignorance of the law excuses one from incurring any criminal liability.
Collectively taken, these situations are defences which do not establish a defence of mistake of law. One of the exceptions is mistake or misapprehension of the civil law, especially when the proof of men's rea is inconsistent with the defendant’s ignorance or mistake.
One example of this situation is in a case where the defendant committed an offence against property and the men's rea of which requires that the defendant did not act with the belief that he is entitled to the property by civil law. Examples of property offence are larceny, theft and robbery.
The mistake of law can relieve any liability where the offence permits it because of its definition. The mistake is allowed and only relevant when it negates Mens rea, and the court recognizes that such a mistake can be pleaded as a defence to raise reasonable doubt to the prosecution’s case.
There are also statutory provisions that provide execution of the general rule that ignorance of the law excuses no one. The exception may be by implication or expressly stated in the statute. Like for example, any legislation which was not brought to the attention of the public can relieve any liability to the offender of the act defined in the said legislation.
Disclaimer : This article is just a summary of the subject matter being discussed and should not be regarded as a comprehensive legal advice for you to defend yourself alone. If you are charged with criminal offences, it is recommended that you seek legal assistance from criminal lawyers.