Lord Sumption at para  said,
The requirements of rationality and proportionality, as applied to decisions engaging the human rights of applicants, inevitably overlap. The classic formulation of the test is to be found in the advice of the Privy Council…in de Freitas v Permanent Secretary of Ministry of Agriculture etc  1 AC 69 , 80. But this decision, although it was a milestone in the development of the law, is now more important for the way in which it has been adapted and applied in the subsequent case law, notably R (Daly) v Sec State for the Home Department  2 AC 532… (Lord Steyn), R v Shayler  1 AC 247 , paras 57–59…, Huang v Sec State for the Home Department  2 AC 167 , 771 para 19 …and R (Aguilar Quila) v Sec State for the Home Department  1 AC 621 , para 45.
Their effect can be sufficiently summarised for present purposes by saying that the question depends on an exacting analysis of the factual case advanced in defence of the measure, in order to determine
(i) whether its objective is sufficiently important to justify the limitation of a fundamental right;
(ii) whether it is rationally connected to the objective;
(iii) whether a less intrusive measure could have been used; and
(iv) whether, having regard to these matters and to the severity of the consequences, a fair balance has been struck between the rights of the individual and the interests of the community. These four requirements are logically separate, but in practice they inevitably overlap because the same facts are likely to be relevant to more than one of them.
… For my part, I agree with the view expressed in this case by Maurice Kay LJ that this debate is sterile in the normal case where the effectiveness of the measure and the degree of interference are not absolute values but questions of degree, inversely related to each other. The question is whether a less intrusive measure could have been used without unacceptably compromising the objective.
Lord Reed JSC, whose judgment I have had the advantage of seeing in draft, takes a different view on the application of the test, but there is nothing in his formulation of the concept of proportionality (see his paras 68–76) which I would disagree with.
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