Individuals who are public office-holders have the capacities that go with the legal personality that they have as natural persons. The Crown is a corporation sole or aggregate and so has general legal capacity, including (subject to some statutory limitations and limitations imposed by European law) the capacity to enter into contracts and to own and dispose of property. The fact of a continued undisputed exercise of a power by a public body is immaterial, unless it points to a customary power exercised from time immemorial.

In particular, the existence of a power cannot be proved by the practice of a private office. (2) The argument of state necessity is not sufficient to establish the existence of a power or duty which would entitle a public body to act in a way that interferes with the rights or liberties of individuals. However, the common law does recognise that in case of extreme urgency, when the ordinary machinery of the state cannot function, there is a justification for the doing of acts needed to restore the regular functioning of the machinery of government. 3) If effect is to be given to the doctrine that the existence or non-existence of a power or duty is a matter of law, it should be possible for the courts to determine whether or not a particular power or duty exists, to define its ambit and provide an effective remedy for unlawful action. The independence of the judiciary is essential to the principle of legality. The right of access to the courts can be excluded by statute, but this is not often done in express terms.

A person whose civil or political ights and freedoms as guaranteed by the Convention for the Protection of Human Rights and Fundamental Freedoms (the European Convention on Human Rights) have been infringed is entitled under the Convention to an effective right of access to the courts and an effective national remedy. On the other hand, powers are often given to bodies other than the ordinary courts, to decide questions of law without appeal to the ordinary courts, and sometimes in such terms that their freedom from appellate jurisdiction extends to their findings of fact or law on which the existence of their powers depends. 4) Since the principal elements of the structure of the machinery of government, and the powers and duties which belong to its several parts, are defined by law, its form and course can be altered only by a change of law. Conversely, since the legislative power of Parliament is unrestricted, save where European Community law has primacy, its form and course can at any time be altered by Parliament. Consequently there are no powers or duties inseparably annexed to the executive government.