Public authorities must act within their powers or they will be acting ultra vires, meaning that they would be acting without legal authority. The powers are usually set out in primary or subordinate legislation.
Limitations on those powers may be set out in legislation, or may be implied by the Court.
Public authorities must also be aware of the further limitations on their powers. These may be under the general public law principles discussed in this guidance, European law, the Human Rights Act 1998, the Equality Act 2010, the Well-being of Future Generations (Wales) Act 2015, the Welsh Language (Wales) Measure 2011 and data protection and freedom of information legislation.
Public authorities have a duty to understand the nature of their powers and their limits, which can be understood by reading the relevant legislation and any accompanying documents.