Sweet v Parsley was an English legal case

English law

English law is the legal system of England and Wales, and is the basis of common law legal systems used in most Commonwealth countries and the United States except Louisiana...

 where the defendant was found guilty of allowing her property to be used for smoking cannabis. Even though she had no knowledge of the offence, it was on her property so she was liable without fault. This conviction was later quashed by the House of Lords

Judicial functions of the House of Lords

The House of Lords, in addition to having a legislative function, historically also had a judicial function. It functioned as a court of first instance for the trials of peers, for impeachment cases, and as a court of last resort within the United Kingdom. In the latter case the House's...

 on the grounds that knowledge of the use of the premises was essential to the offence. Since she had no such knowledge, she did not commit the offence.

It is significant in English criminal law as it sets out a new set of guidelines for determining strict liability

Strict liability (criminal)

In criminal law, strict liability is liability for which mens rea does not have to be proven in relation to one or more elements comprising the actus reus although intention, recklessness or knowledge may be required in relation to other elements of the offence...

. Lord Reid

James Reid, Baron Reid

James Scott Cumberland Reid, Baron Reid, CH, KC FRSE was a Scottish Unionist politician and judge. His reputation is as one of the most outstanding judges of the 20th century....

 laid down the following guidelines for all cases where the offence is criminal as opposed to quasi-criminal:

1. Wherever a section is silent as to mens rea
   Mens rea
   Mens rea is Latin for "guilty mind". In criminal law, it is viewed as one of the necessary elements of a crime. The standard common law test of criminal liability is usually expressed in the Latin phrase, actus non facit reum nisi mens sit rea, which means "the act does not make a person guilty...
   
   there is a presumption that, in order to give effect to the will of Parliament, words importing mens rea must be read into the provision.
2. It is a universal principle that if a penal provision is reasonably capable of two interpretations, that interpretation which is most favourable to the accused must be adopted.
3. The fact that other sections of the Act expressly require mens rea is not in itself sufficient to justify a decision that a section which is silent as to mens rea creates an absolute offence. It is necessary to go outside the Act and examine all relevant circumstances in order to establish that this must have been the intention of Parliament.