 The constitutional theory of judicial review has long been dominated by the doctrine of "ultra vires", under which a decision of a public authority can only be set aside if it exceeds the powers granted to it by Parliament.The role of the courts was seen as enforcing the "will of Parliament" in accordance with the doctrine of Parliamentary sovereignty.However, the doctrine has been widely interpreted to include errors of law and of fact and the courts have also declared the decisions taken under the Royal Prerogative to be amenable to judicial review.