Decision-makers will be acting outside of their powers if they act in a way that is inconsistent with the purpose of the legislation that gives them their power. By way of example, the House of Lords held in the Stewart v Perth and Kinross Council [2004) UKHL 16 case that the purpose of Part II of the Civic Government (Scotland) Act 1982 was not to allow local authorities in Scotland to require second hand car dealers to give specific information to car buyers about the condition of the cars. However commendable the local authority’s intention was in trying to protect consumers by requiring dealers to provide this information, that was not Parliament’s intention when it passed the 1982 Act and the requirement was unlawful.
In some circumstances, the courts will require a public authority to exercise its discretion in a particular way if failing to do so would be inconsistent with the purpose of the legislation. (Padfield v Minister of Agriculture, Fisheries and Food  AC 997).