Public authorities must identify their relevant powers and must act within the limits of these powers or they will be acting ultra vires, meaning that they would be acting without legal authority. A legal power to do something will usually be found in legislation – either in primary legislation (an Act of Parliament (e.g. the Serious Crime Act 2015) or an Act of the National Assembly for Wales (e.g. the Historic Environment (Wales) Act 2016) or in subordinate legislation (e.g. statutory instruments such as orders or regulations (for instance the Council Tax Reduction Schemes and Prescribed Requirements (Wales) Regulations 2013).
Decision-makers should consider the wording of the relevant legislation to understand the limits and purposes of the power. In some cases, the clearest indication of the legislation’s purpose may be found in accompanying documents such as a report that gave rise to the legislation, the report of a committee of the National Assembly or Parliament, the explanatory notes that accompany the relevant legislation or the record of proceedings in Parliament or the National Assembly.