“17. It is one thing to say that consideration of a possible alternative site is a potentially relevant issue, so that a decision-maker does not err in law if he has regard to it. It is quite another to say that it is necessarily relevant, so that he errs in law if he fails to have regard to it … “17. It is one thing to say that consideration of a possible alternative site is a potentially relevant issue, so that a decision-maker does not err in law if he has regard to it. It is quite another to say that it is necessarily relevant, so that he errs in law if he fails to have regard to it … 18. For the former category the underlying principles are obvious. It is trite and long-established law that the range of potentially relevant planning issues is very wide (Stringer v Minister of Housing and LocalGovernment[1970] 1 WLR 1281 ); and that, absent irrationality or illegality, the weight to be given to such issues in any case is a matter for the decisionmaker (Tesco Stores Ltd v Secretary of State for the Environment and WestOxfordshire District Council[1995] 1 WLR 759 , 780). On the other hand, to hold that a decision-maker has erred in law by failing to have regard to alternative sites, it is necessary to find some legal principle which compelled him (not merely empowered) him to do so.” 31. I referred to the discussion of this issue in a different context by Cooke J in the New Zealand Court of Appeal, in CreedNZ Inc v Governor General[1981] 1 NZLR 172 , 182 (adopted by Lord Scarman in the House of Lords in In re Findlay[1985] AC 318 , 333-334, and in the planning context by Glidewell LJ in BoltonMetropolitan Borough Council v Secretary of State for the Environment andGreater Manchester Waste Disposal Authority(1991) 61 P & CR 343 , 352): “26. Cooke J took as a starting point the words of Lord Greene MR in the Wednesbury case[1948] 1 KB 223 , 228: ‘If, in the statute conferring the discretion there is to be found expressly or by implication matters which the authority exercising the discretion ought to have regard to, then in exercising the discretion it must have regard to those matters.’ He continued: ‘What has to be emphasised is that it is only when the statute expresslyor impliedly identifies considerations required to be taken into accountby the authority as a matter of legal obligation that the court holds a decision invalid on the ground now invoked. It is not enough that it is one that may properly be taken into account, nor even that it is one which many people, including the court itself, would have taken into account if they had to make the decision ...’ (Emphasis added) ‘If, in the statute conferring the discretion there is to be found expressly or by implication matters which the authority exercising the discretion ought to have regard to, then in exercising the discretion it must have regard to those matters.’ He continued: ‘What has to be emphasised is that it is only when the statute expresslyor impliedly identifies considerations required to be taken into accountby the authority as a matter of legal obligation that the court holds a decision invalid on the ground now invoked. It is not enough that it is one that may properly be taken into account, nor even that it is one which many people, including the court itself, would have taken into account if they had to make the decision ...’ (Emphasis added) 27. In approving this passage, Lord Scarman noted that Cooke J had also recognised, that - ‘… in certain circumstances there will be some matters so obviously material to a decision on a particular project that anything short of direct consideration of them by the ministers … would not be in accordance with the intention of the Act.’ (In re Findlay at p 334) 28. It seems, therefore, that it is not enough that, in the judge’s view, consideration of a particular matter might realistically have made a difference. Short of irrationality, the question is one of statutory construction. It is necessary to show that the matter was one which the statute expressly or impliedly (because ‘obviously material’) requires to be taken into account ‘as a matter of legal obligation’.”