The courts will always start with the presumption that mens rea is required, but if they decide that the offence doesn't require mens rea for part of the actus reus, then the offence is once of strict liability
Strict liability - there is no requirement for mens rea for all of the actus reus
PHARMACEUTICAL SOCIETY OF GREAT BRITAIN v STORKWAIN LTD (1986) - Pharmacist hadn't realised that a prescription was a forgery. Supplying drugs without a genuine prescription made them guilty of the offence, even though the forgery was very difficult to spot
