While there is a voluminous literature on proportionality, there is considerably less on reasonableness as a test for judicial review of discretionary determinations. This paper examines the nature of reasonableness as a test for judicial review of discretion in UK law. The paper is not predicated on the assumption that reasonableness always bears the same meaning whenever it is used in constitutional and administrative law in any legal system.Craig's focus is on reasonableness in the context of review of exercises of discretion (rather than, for example, the unified reasonableness standard that Canadian courts (supposedly...) apply to both interpretations of law and exercises of discretion).
Subject to this caveat, it is argued that reasonableness as a test for judicial review of discretion in UK law is concerned with review of the weight and balance accorded by the primary decision-maker to factors that have been or can be deemed relevant in pursuit of a prima facie allowable purpose; that this is borne out through examination of the case law; that insofar as incommensurability is perceived to be a problem in the context of proportionality then this is also true in relation to reasonableness review; that the incommensurability problem is less problematic than is commonly perceived; and that a proper appreciation of reasonableness review has implications for the debate concerning reasonableness and proportionality as tests for judicial review in administrative law.
Craig's detailed discussion of weight, balance and incommensurability makes the paper an important contribution to understanding the nature of reasonableness review, a topic that has generally received scant attention. For those interested in reading further, I set out my preferred approach in a 2011 article and, in more detail, in chapter 4 of A Theory of Deference in Administrative Law.