"The rule of law has a number of different meanings and corollaries. Its primary meaning is that everything must be done according to law. Applied to the powers of government, this requires that every government authority which does some act which would otherwise be a wrong (such as taking a man's land), or which infringes a man's liberty (as by refusing him planning permission), must be able to justify its action as authorized by law -- and in nearly every case this will mean authorized by Act of Parliament. ... But the rule of law demands something more, since otherwise it would be satisfied by giving the government unrestricted discretionary powers, so that everything that they did was within the law. ... The secondary meaning of the rule of law, therefore, is that governments should be conducted within a framework of recognized rules and principles which restrict discretionary power. ... Thus the Home Secretary has a nominally unlimited power to revoke any television licence and a local planning authority may make planning permission subject to such conditions as it thinks fit, but the courts will not allow these powers to be used in ways which Parliament is not thought to have intended. ... Faced with the fact that Parliament freely confers discretionary powers with little regard to the dangers of abuse, the courts must attempt to strike a balance between the needs of fair and efficient administration and the need to protect the citizen against arbitrary government. ...
What the rule of law demands is not that wide discretionary power should be eliminated, but that the law should be able to control its exercise. ... The first requirement is the recognition that all power has legal limits. The next requirement, no less vital, is that the courts should draw those limits in a way which strikes the most suitable balance between executive efficiency and legal protection of the citizen. Parliament constantly confers upon public authorities powers which on their face might seem absolute and arbitrary. But arbitrary power and unfettered discretion are what the courts refuse to countenance. They have woven a network of restrictive principles which require statutory powers to be exercised reasonably and in good faith, for proper purposes only, and in accordance with the spirit as well as the letter of the empowering Act. They have also, as explained elsewhere, imposed stringent procedural requirements."16

"The discretion of a statutory body is never unfettered. It is a discretion which is to be exercised according to law. That means at least this: the statutory body must be guided by relevant considerations and not by irrelevant. If its decision is influenced by extraneous considerations which it ought not to have taken into account, then the decision cannot stand. No matter that the statutory body may have acted in good faith, nevertheless the decision will be set aside. ..."17