Sweet v Parsley

Sweet v Parsley was an English criminal law case where the defendant landlady of a farmhouse (which was let to students and which she visited infrequently) was charged under a 1965 Act "of having been concerned in the management of premises used for smoking cannabis".
Even though she had neither knowledge of nor privity with the offence, it took place on her property and at first instance she was convicted, being deemed "liable without fault". This conviction was later quashed by the House of Lords 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.
Requirement of "mens rea".
Lord Reid declared:
. . . there has for centuries been a presumption that Parliament did not intend to make criminals of persons who were in no way blameworthy in what they did. That means that whenever a section is silent as to "mens rea" there is a presumption that, in order to give effect to the will of Parliament, we must read in words appropriate to require "mens rea". . . . it is firmly established by a host of authorities that "mens rea" is an essential ingredient of every offence unless some reason can be found for holding that that is not necessary.
The case's significance in English criminal law is that it sets out new set guidelines for determining whether an offence is one of strict liability or whether "mens rea" is a presumed requirement.
Lord Reid laid down the following guidelines for all cases where the offence is criminal as opposed to quasi-criminal: