(ii) irrationality and (iii) procedural impropriety. This is how he put it: By ‘illegality’ as a ground for judicial review I mean that the decision maker must understand directly the law that regulates his decision making power and must give effect to it. Whether he has or not is par excellence a justiciable question to be decided in the event of a dispute, by those S/N nLh1tzyYkabfvXIUkqC4Q persons, the Judges, by whom the judicial power of the state is exercisable. By ‘irrationality’ I mean what can by now be succinctly referred to as ‘Wednesbury unreasonableness’ (see Associated Provincial Picture Houses Limited v. Wednesbury Corporation [1948] 1 KB 223). It applies to a decision which is so outrageous in its defiance of logic or of accepted moral standards that no sensible person who had applied his mind to the question to be decided could have arrived at it. Whether a decision falls within this category is a question that Judges by their training and experience should be well equipped to answer, or else there would be something badly wrong with our judicial system. To justify the Courts’ exercise of this role, resort I think is today no longer needed to Viscount Radcliffe’s ingenious explanation in Edwards (Inspector of Taxes) v. Bairstow [1956] AC 14, of irrationality as a ground for a Court’s reversal of a decision by ascribing it to an inferred though undefinable mistake of law by the decisionmaker. ‘Irrationality’ by now can stand on its own feet as an accepted ground on which a decision may be attacked by judicial review. I have described the third head as ‘procedural impropriety’ rather than failure to observe basic S/N nLh1tzyYkabfvXIUkqC4Q rules of natural justice or failing to act with procedural fairness towards the person who will be affected by the decision. This is because susceptibility to judicial review under this head covers also failure by an administrative tribunal to observe procedural rules that are expressly laid down in the legislative instrument by which its jurisdiction is conferred, even where such failure does not involve any denial of natural justice. Lord Diplock also mentioned ‘proportionality’ as a possible fourth ground of review which called for development. Lord Diplock’s first ground for challenge, namely, ‘illegality’, involves insisting that the authority or body whose decision is being impugned has kept strictly within the perimeters of their powers. A good example of this is the case of Westminster City Council v. Great Portland Estates plc. [1985] AC 661, an ultra vires case, involving judicial construction of the Town and Country Planning Act 1971. The question for decision was whether the Act permitted the relevant authorities, by resort to their development plans, to support the retention of traditional industries or was the ambit of the Act such as to permit only ‘land use’ aims to be pursued? It was held that ‘the character of the use of the land, not the particular purpose of a particular occupier’ was the concern of planning and, therefore the authority S/N nLh1tzyYkabfvXIUkqC4Q could not seek to favour any particular occupant or class of occupant. By thus confining the relevant authority strictly to the four walls of the powers conferred upon them by the Act, the Court was involved in the exercise of reviewing the impugned decision for substance and not just process. Lord Diplock’s second ground for challenge, namely, ‘irrationality’ recognises a different route whereby the substance of a decision may be reviewed by the Courts. By this means, Lord Diplock made it clear that despite being legal, that is to say within the powers conferred, a decision may nevertheless, be struck down, for being contrary to substantive principles. In the words of Lord Diplock, ‘a decision which is so outrageous in its defiance of logic or of accepted moral standards that no sensible person who had applied his mind to the question to be decided could have arrived at it’.”.