a) When a statute confers power upon a public official to destroy or prejudice a person's rights, interests or legitimate expectations, the rules of natural justice regulate the exercise of that power unless they are excluded by the plain words of necessary intendment."
Annetts v McCann (1990 170 CLR 596 )Mason CJ Deane and McHugh JJ (at 598)

b) The effect of a failure to observe the rules of procedural fairness natural justice is to render a decision void see for example Dixon v Commonwealth of Australia (1980) 3 ALD 289 where the Fed Court of Australia (Bowen CJ Deane and Kelly JJ) held, inter alia

(a) Where a statute confers power to make a decision affecting the rights, property or legitimate expectations of a person, the rules of natural justice or the standards of fairness recognised by common law will prima facie be applicable…If the applicable rules or standards are not observed it is not relevant to inquire whether or not the decision was a correct one. If that decision adversely affects the rights, property or legitimate expectations of a person denied natural justice, the decision will at least to that extent be void.

(b) In the forefront of the rules of natural justice which are prima facie applicable to the exercist of such a statutory power, there lies the obligation to give to a party liable to be directly affected by the decision, the opportunity of being heard. Here agai, the precise scope of the obligation will vary according to the nature of the decision and the circumstances of the case. Ordinarily, in a case where a statutory decision depriving a particular individual of property, rights or legitimate expectations is in contemplation of the obligation to extend to him the opportunity of being heard will involve ensuring that he is given the opportunity of ascertaining the relevant issues, and being informed of the nature and content of the material which is being considered against him.

(c) A legislative intent to exclude the established common law standards of fairness must be established, as a matter of constructipon, by th express words or clear intendment of the legislation conferring the relevant power…"