Here are some choice extracts, with some highlighting:
A better starting point, I think, is another insight offered by Taggart, according to which public law is increasingly about the enforcement of a “culture of justification”...
Against this background, several questions need to be posed about the notion of justification. Most obviously, it is meaningless to ask whether a given decision or policy is justified unless we articulate the standards against which the measure is to be evaluated. At the very least (leaving third-source considerations to one side for present purposes) there will be a need to demonstrate positive legal authority. But if particularly valuable norms, such as the rights or legitimate expectations of the individual, are impinged upon then the sufficiency of any justification may fall to be assessed against additional, more demanding criteria. It is also important to be clear about two further matters. First, when we say that a decision must be justified by reference to a given benchmark, what does that really mean? It presumably means something more exact (and, normally, something less) than that the court has to be satisfied that it too would have proceeded in the way that the administrator did. The nature of justification is, in this sense, tied up with considerations about the standard of review—which, in turn, relates back to an assessment of the normative significance of the value impugned by the decision and hence the appropriate scale of the decision-maker’s justificatory burden. Second, even once the issue of the standard of justification, or review, has been settled, questions will arise about whether that standard has been met—which, in turn, triggers questions about the court’s role in evaluating the quality of any justifications offered by the decision-maker.
My argument is that it is necessary to move beyond a doctrinal focus which results (depending upon one’s preferences) in either a bifurcated approach or one wedded to a specific doctrine (e.g. proportionality), and to concentrate instead on calibrating substantive review by reference to the normative and institutional considerations which ought properly to shape it. I readily acknowledge that this approach may sometimes—perhaps often—produce outcomes that do not, at least superficially, differ radically from the position that would obtain according to the conventional wisdom. I am certainly not suggesting that the courts invariably, or even often, get it wrong. The difference, however, is one of emphasis. The aim is to secure a framework that is better equipped to enable the courts to get it right, and one that is shaped from the bottom up by the relevant normative and institutional factors. Doctrine should be the servant of such considerations, not a procrustean bed into which they have to be shoehorned.
First, the court will have to determine what should constitute the operative standard of justification in the particular circumstances of the case. What, in other words, should be the justificatory burden under which the decision-maker is placed, and which will have to be discharged if the decision is to be found by the reviewing court to be lawful? The proportionality versus rationality debate captures something of this matter—but only in a rudimentary fashion. On the face of it, asking whether a decision is proportionate is different from—and subjects the decision-maker to a more demanding justificatory burden than—asking whether it is merely rational. However, just as proportionality and rationality are distinguishable, so are distinctions—justificatory gradations—concealed within those concepts. The “sub-Wednesbury” and “super-Wednesbury” notions have long been evidence of this in relation to the rationality doctrine, as also is the more recently-developed “cogent reasons” concept. The point is obvious too in relation to proportionality, which can be (and is) deployed in more and less demanding ways. For instance, the requirement that a given measure be a “necessary” means of advancing a legitimate aim does not always mean what it says, in that the necessity criterion does not invariably rule out every option save that which is the least restrictive of the compromised right or other norm.
When the court rolls up its sleeves and begins to confront questions of this nature, considerations about the intensity of review—and deference—necessarily shift from the abstract to the particular. The setting of the burden of justification (or of the starting-point level of deference) is undertaken on the basis of an all-other-things-being-equal assessment of the nature and importance of the compromised norm. The reality, however, is that all other things are often not equal, such that the court’s analysis of whether the operative standard of justification has been met may need to be moderated by reference to considerations of adjudicative deference. Starting-point deference is then about determining the onerousness of the decision-maker’s justificatory burden; adjudicative deference, in contrast, is relevant when the court is determining whether that burden has actually been discharged.I have written a little on similar themes: see "Defining Deference" here.
Acknowledging that there are (at least) two stages at which deference (and the considerations that underpin it) can play a role is important. In both determining the standard of review -- correctness, reasonableness, proportionality, etc -- and in the application of the standard, it is possible for reviewing courts to be deferential. In applying a standard of reasonableness (doctrinal deference), some weight (epistemic deference) might be given to a decision-maker's identification of the interests relevant to making a decision. Of course, there is a danger of double counting in these situations. If we decide on the basis of various considerations that deference is appropriate in determining the standard of review, it might not be appropriate to return to those same considerations and tilt the balance further in favour of the decision-maker.
But, as Mark suggests, we should not be slaves to technical arguments about doctrine. Most of the hard cases that public lawyers have to address involve situations in which the "reasonableness" or "proportionality" of a decision is not clear one way or the other. The real question is whether the "burden of justification" has been discharged: has the decision-maker convinced the reviewing court that, despite appearances, its position is justified? We need to ask what the relevant considerations are in answering this question. Plainly, it is necessary to drill down underneath concepts like "reasonableness" and "proportionality" and identify their true foundations in order to understand how public law judges decide and how they ought to decide.