Some cases end up deciding much more in retrospect than they did at the time they were decided. The case of Anisminic  2 AC 147 (HL) comes to mind as one of the clearest examples of such a case in public law, with later courts taking the judgment to be grounds to abandon the distinction between jurisdictional error and non-jurisdictional error. Half a century on from Anisminic, the Supreme Court’s decision in Miller/Cherrylikewise contains the potential for the abandonment of a key conceptual distinction in public law—this time the distinction between judicial review with respect to the existence and scope of a power on the one hand and the manner of its exercise on the other hand, in the process dispensing with the troublesome concept (troublesome at least to a certain kind of public lawyer) of justiciability. However, whether Miller/ Cherryends up joining Anisminicas a truly revolutionary case or whether it remains a ‘one-off’ confined to the maelstrom of Brexit will depend on what future courts choose to do with it. As the cliché would have it, only time will tell.
What the Supreme Court did in Miller/ Cherry was effectively engage in review of the manner of the exercise of a prerogative by declaring that it was merely engaging in review for the (logically prior questions of the) existence and scope of the asserted prerogative. No longer was the question for the court “Was the Prime Minister’s advice to the Queen to prorogue Parliament unlawful?”. Instead, the question the Supreme Court chose to answer was in effect: “Did the (purported) prorogation come within the scope of the prerogative power to prorogue?” —in other words, was this purported prorogation an actualprorogation (within the legal meaning of that word) or was it in fact something else entirely, outside the scope of the power altogether?
The courts below (both in Scotland and in England and Wales) were agreed that this was a case about the manner of the exercise of the prerogative to prorogue (the central question being whether something which was undoubtedly a prorogation was done for an improper purpose); where they disagreed was whether such a dispute was justiciable in a court of law. The Supreme Court, on the other hand, reconceptualised the whole dispute as a question about the existence and scope of the power to prorogue. No longer was the question “was this prorogation improper?” but rather “was this a prorogation at all”? On the one hand such an approach certainly avoids questions of non-justiciability and the (political) difficulty of a court holding that the Prime Minister acted for an improper purpose in advising the Queen to prorogue Parliament. But at what cost? The Supreme Court showed that it is possible, with enough judicial will to fly in the face of reality and hundreds of years of understanding of what the prerogative to prorogue means, to redefine a dispute about the manner of the exercise of a power into one about the power’s extent and scope. In the Humpty-Dumpty world of UK Supreme Court adjudication any question about the manner of the exercise of a power (well, certainly of a prerogative power but with enough judicial ingenuity there is no reason why the Court’s approach couldn’t also be extended to statutory powers as well) can potentially be reconceptualised as a question about the existence and scope of a power. As if by magic, questions about non-justiciability all disappear into the ether never to trouble judges again (unless of course the judges don’t want to resolve the issue in the case at hand in which case they might conveniently rediscover the concept of non-justiciability and notions of judicial restraint).
Dr David Tomkins is Lecturer in Law, University of Newcastle, Australia