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Blackmail is an offence under section 21 of the Theft Act (1968). The actus reus of the offence is the making of a demand with menaces. What amounts to a demand can be implied from the circumstances (Collister v Warhurst 1955). The jury should not be given any further direction on the meaning of menaces, unless the victim is particularly vulnerable or timid (R v Garwood 1987).

The mens rea of the offence requires that the demand be unwarranted. The demand is not unwarranted if the defendant belives that he has reasonable grounds for making the demand or the use of the menaces is a proper means of enforcing the demand. This will never be so if the demand is a criminal act (R v Harvey 1981). The mens rea also requires an intention to make a gain for himself or another or to cause a loss to another. This must be measured in money or other property and can include keeping what one has or not getting what one might get (section 34(2) of the Theft Act (1968)).