“When, in Secretary of State for Education and Science v. Tameside Metropolitan Borough Council [1977] A.C. 1014, the precise meaning of "unreasonably" in an administrative context was crucial to the decision, the five speeches in the House of Lords, the three judgments in the Court of Appeal and the two judgments in the Divisional Court all succeeded in avoiding needless complexity. The simple test used throughout was whether the decision in question was one which a reasonable authority could reach. The converse was described by Lord Diplock, at p. 1064, as "conduct which no sensible authority acting with due appreciation of its responsibilities would have decided to adopt." These unexaggerated criteria give the administrator ample and rightful rein, consistently with the constitutional separation of powers.”