R (on the application of Bibi) v London Borough of Newham;  EWCA Civ 607;  1 WLR 237 (CA).
 In all legitimate expectation cases, whether substantive or procedural, three practical questions arise. The first question is to what has the public authority, whether by practice or by promise, committed itself; the second is whether the authority has acted or proposes to act unlawfully in relation to its commitment; the third is what the court should do. This formulation of the questions is we think a more helpful way of approaching the problems in this type of case than the fivefold question adopted during argument.
To what has the authority committed itself?
 The answer to the first is a question of analysing the evidence - it poses no jurisprudential problems.
 Sometimes, as in the first category of outcome analysed in Ex p Coughlan  2 WLR 622 (para 57) the answer to this first question is dispositive of the case. It seems to us that the present authorities in that group of cases (in particular In re Findlay  AC 318,  3 All ER 801 at p 338 of the former report) make it generally appropriate to allocate the issue of legitimacy to this initial question. In other words, if the public body has done nothing and said nothing which can legitimately have generated the expectation that is advanced to the court, the case ends there. It seems likely that a representation made without lawful power will be in this class. In the present case the answer to the first question is not in dispute and is in favour of the applicants.
The interrelation of the second and third questions
 Two problems face a court in answering these questions. The first is to find one or more measuring rods by which it can be objectively determined whether a certain action or inaction is an abuse of power. The second is what order to make once an abuse of power has been discerned - can the court come to a substantive decision itself or should it send the matter back to the decision taker to decide afresh according to law?
 To a degree the answer to the second depends on the approach one takes to the first. As Laws LJ pointed out in R v Secretary of State for Education and Employment ex parte Begbie  1 WLR 1115 at p 1131C
'The more the decision challenged lies in what may inelegantly be called the macro-political field, the less intrusive will be the court's supervision. More than this: in that field, true abuse of power is less likely to be found, since within it changes of policy, fuelled by broad conceptions of the public interest, may more readily be accepted as taking precedence over the interests of groups which enjoyed expectations generated by an earlier policy.'
Has the authority acted unlawfully?
 As Professor Craig makes clear in his perceptive discussion of this topic in Ch 19 of the fourth edition of his 'Administrative Law', it is important to recognise that there is often a tension between several values in these cases. A choice may need to be made as to which good we attain and which we forego. There are administrative and democratic gains in preserving for the authority the possibility in the future of coming to different conclusions as to the allocation of resources from those to which it is currently wedded. On the other hand there is value in holding authorities to promises which they have made, thus upholding responsible public administration and allowing people to plan their lives sensibly. The task for the law in this area is to establish who makes the choice of priorities and what principles are to be followed.
 Several attempts have been made to find a formulation which will provide a test for all cases. However, history shows that wide-ranging formulations, while capable of producing a just result in the individual case, are seen later to have needlessly constricted the development of the law. Thus it was the view of this court in Coughlan  2 WLR 622 that a principle, apparently earlier embraced by this court in R v Secretary of State for the Home Department, ex parte Hargreaves  1 All ER 397,  1 WLR 906, to the effect that the court would only enforce expectations as to procedure as opposed to expectations of a substantive benefit, was wrongly framed.
Has the authority acted unlawfully? The relevance of reliance on the promise.
 [Counsel for Newham] submits that, in cases where the expectation which has been generated is of a substantive as opposed to a procedural benefit, authority limits the court to enforcing it only if (a) the motive for resiling from it was improper, or (b) there has been detrimental reliance on it. Only then, he submits, can the departure be said to amount, as it must, to an abuse of power. Founding on the distinction between procedural and substantive expectations identified in Coughlan para 57, on the reasoning in Ex p Preston  AC 835, 866-7 and on the cases reported to date, he argues that (absent bad faith) a substantive legitimate expectation can only arise where a situation analogous to a private law wrong, and therefore involving detrimental reliance, exists.
 We would not accept this formulation. As Sir Thomas Bingham MR observed in R v IRC, ex parte Unilever plc  STC p 681, 68 Tax Cas 205 at p 690f of the former report:
'The categories of unfairness are not closed, and precedent should act as a guide and not as a cage.'
 As indicated in R v Secretary of State for Education and Employment, ex parte Begbie  1 WLR 1115, reliance, though potentially relevant in most cases, is not essential. In that case a letter sent to the parents of one child affected by legislative and policy changes concerning assisted school places came to the knowledge of another child's parent, who relied on it in judicial review proceedings. Peter Gibson LJ, giving the leading judgment, said at p 1123H:
'Mr. Beloff submits . . . (v) it is not necessary for a person to have changed his position as a result of such representations for an obligation to fulfil a legitimate expectation to subsist; the principle of good administration prima facie requires adherence by public authorities to their promises. He cites authority in support of all these submissions and for my part I am prepared to accept them as correct, so far as they go. I would however add a few words by way of comment on his fifth proposition, as in my judgment it would be wrong to understate the significance of reliance in this area of the law. It is very much the exception, rather than the rule, that detrimental reliance will not be present when the court finds unfairness in the defeating of a legitimate expectation.'
 In the light of this, we respectfully adopt what Professor Craig has proposed in this regard in his Administrative Law at p 619:
'Detrimental reliance will normally be required in order for the claimant to show that it would be unlawful to go back on a representation. This is in accord with policy, since if the individual has suffered no hardship there is no reason based on legal certainty to hold the agency to its representation. It should not, however, be necessary to show any monetary loss, or anything equivalent thereto.'
 But he gives the following instance of a case where reliance is not essential:
'Where an agency seeks to depart from an established policy in relation to a particular person detrimental reliance should not be required. Consistency of treatment and equality are at stake in such cases, and these values should be protected irrespective of whether there has been any reliance as such.'
 In our judgment the significance of reliance and of consequent detriment is factual, not legal. In Begbie  1 WLR 1115 both aspects were in the event critical: there had been no true reliance on the misrepresentation of policy and therefore no detriment suffered specifically in consequence of it. In a strong case, no doubt, there will be both reliance and detriment; but it does not follow that reliance (that is, credence) without measurable detriment cannot render it unfair to thwart a legitimate expectation.
 The traditional view has been that the Wednesbury categories were exhaustive of what was an abuse of power. However in Coughlan  2 WLR 622 the court preferred 'to regard the Wednesbury categories as the major instances (not necessarily the sole ones . . . ), of how public power may be misused' (para 81).
 In Coughlan the court followed R v IRC ex parte Unilever  STC 681, 68 Tax Cas 205 in asking itself whether the reneging by an authority on its promise was 'so unfair as to amount to an abuse of power' (para 78 of the former report). It concluded that it was. However, without refinement, the question whether the reneging on a promise would be so unfair as to amount to an abuse of power is an uncertain guide.
 Where one is dealing with a promise made by an authority a major part of the problem is that it is often not adequate to look at the situation purely from the point of view of the disappointed promisee who comes to the court with a perfectly natural grievance.
 Sometimes many promises have been made to many different persons each of which has induced a reasonable expectation of a substantive benefit for that person but all of which promises cannot be fulfilled. This situation is not uncommon in central and local Government. Decision takers promise and find themselves unable to deliver that which they have promised. As Bacon, perhaps cynically, remarked 400 years ago 'it is a certain sign of wise government and proceeding that it can hold men's hearts by hopes when it can not by satisfaction'. Seen from the point of view of administrators focusing on the problem immediately before their eyes a promise seems reasonable or will at least reduce the need to worry further in the immediate future about the promisee. But when they, or their superiors, focus on a wider background it appears that the making of the promise was unwise or that, in any event, its fulfilment seems too difficult.
 Thus in cases such as those before the court, the family with the highest points on the Authority's scale can be regarded as having a legitimate expectation that the next five bedroom flat would go to them. So can the applicant who was promised a five bedroom flat within 18 months which have elapsed. So can all the other persons who have been promised suitable accommodation within 18 months. Yet the Authority does not possess enough housing for them all.
 The suggestion was made in argument that this problem can be avoided by the authority which is short of housing giving every family enough money to provide its own housing. But this is not always an escape from the problem because the money can often not be found without depriving others of money which they expected to retain or of benefits which they expected to receive.
 But on any view, if an authority, without even considering the fact that it is in breach of a promise which has given rise to a legitimate expectation that it will be honoured, makes a decision to adopt a course of action at variance with that promise then the authority is abusing its powers.
The role of the court
 The court has two functions - assessing the legality of actions by administrators and, if it finds unlawfulness on the administrators' part, deciding what relief it should give. It is in our judgment a mistake to isolate from the rest of administrative law cases those which turn on representations made by authorities. The same constitutional principles apply to the exercise by the court of each of these two functions.
 The court, even where it finds that the applicant has a legitimate expectation of some benefit, will not order the authority to honour its promise where to do so would be to assume the powers of the executive. Once the court has established such an abuse it may ask the decision taker to take the legitimate expectation properly into account in the decision making process.
 Only part of the relevant material upon consideration of which any decision must be made is before the court. Because of the need to bear in mind more than the interests of the individual before the court, relevant facts are always changing. As Lord Bingham said in R v Cambridge Health Authority, ex parte B  2 All ER 129,  1 WLR 898:
'. . . it would be totally unrealistic to require the authority to come to the court with its accounts and seek to demonstrate that if this treatment were provided for B then there would be a patient, C, who would have to go without treatment. No major authority could run its financial affairs in a way which would permit such a demonstration.'
 While in some cases there can be only one lawful ultimate answer to the question whether the authority should honour its promise, at any rate in cases involving a legitimate expectation of a substantive benefit, this will not inevitably be the case.