The moment the Supreme Court announced its astonishing judgment against the Prime Minister’s advice to prorogue Parliament, the public law spin machine went into action.

It is a central fiction of common law that judges make ‘discoveries’, rather than decisions. The law has somehow always existed as the judges interpret it, even in the case of the most surprising judgments.

But as I wrote in the Daily Telegraph, the sheer speed with which this case was brought has undermined the manufacture of this myth:

“Normally this retrospective revision of received wisdom takes place over time, aided by little sustained interest in the evolution of public law from either politicians or the media. Here instead the entire process has taken place amid the full glare of public scrutiny, and legal commentators have been forced to perform a complete u-turn on the legal viability of Gina Miller’s case in less than a fortnight.”

There is something slightly absurd about the speed with which this ‘ret-conning’ has taken place. One would scarcely know, from reading yesterday’s reactions, that it was only this month when the High Court comprehensively rejected Gina Miller’s legal challenge, or that that case was heard by three of the country’s most senior judges outside the Supreme Court (the Lord Chief Justice of England and Wales, the Master of the Rolls, and the President of the Queen’s Bench Division).

Were the Supreme Court’s decision as obvious and inevitable as is now pretended, that ruling would have been met with outrage. Yet it wasn’t, because it represented the orthodox understanding of the constitution.

For the legal case for disagreeing with yesterday’s judgment the best I have seen is this one, by Charles Day in the Spectator. He explains the way the judges effectively invented a statute, and the thinness of the historical precedents cited in their piece.

Meanwhile on this site Sir Stephen Laws has set out how the Court failed to factor the conduct of Parliament into its assessment of the constitutional balance of power. (This is apparently a fairly common judicial blindspot as Lord Sumption also failed to address it in his article for today’s Times.)

He is right to point out that the judges were not protecting Parliament from an over-mighty executive – as they might have been had Johnson been trying to evade a vote of no confidence – but are instead buttressing a recalcitrant House of Commons which refuses, for pure political advantage, to wield the proper tools at its disposal for disposing of a government.

Personally I have set out elsewhere how I think that this case could yet provide sceptics of judicial overreach with their ‘Maastricht moment’, a galvanising shock which hardens a tendency into a movement.

But no element of the constitution exists in isolation, and the past 24 hours have shown that some of those who support yesterday’s ruling are trying to wield it in ways which make the common law fiction of retro-active inevitability not just absurd, but sinister, because it is fuelling calls for what amounts to retroactive justice.

This is most apparent in Sir Keir Starmer’s call for Geoffrey Cox to “consider his position” for having provided the Prime Minister with legal advice which turned out to be inaccurate – despite his opinion reflecting the overwhelming consensus at the time and having been upheld in the courts of both England & Wales and Northern Ireland prior to the Supreme Court’s verdict.

It can be seen too in the outrage which has met Boris Johnson and Robert Buckland, for example, saying that whilst the recognise that yesterday’s judgment is the law, they disagree with it. Some of their critics are making the case that you cannot legitimately disagree with – not defy – the judiciary.

For people who claim to be motivated by concerns about capricious and unaccountable power, this combination of attitudes is telling. It would lend to the courts some of the worst features of a pre-modern monarch, with citizens and ministers not only at legal risk from retroactive justice but also forbidden from criticising it by a form of lèse-majesté. When I previously compared the Supreme Court’s advocates to 21st-century Cavaliers I didn’t imagine they would take me so literally.

The myth-making which is central to Common Law ideology exacerbates this problem because it generates a fiction of infallibility and encourages herding on the part of lawyers and informed commentators, which then strengthens the fiction in a vicious cycle.

We can see evidence of this in the suggestion that the Supreme Court’s decision was unanimous not because all eleven judges actually agreed with the reasoning in the judgment, but because those who did not chose to row in behind the majority in order to maximise the power of the result. If true they have denied both the public and the historical record their true opinion, sacrificing a truer reflection of the balance of legal opinion in order to bolster their institution.

This herding tendency can also be seen in Lord Sumption’s op-ed today. It is indeed remarkable that the man who delivered the controversial Reith Lecture ‘Law’s Expanding Empire‘, and published only last month a book on ‘law and the decline of politics’, should accuse the Prime Minister of “constitutional vandalism”. But it is even more remarkable given that he himself was arguing less than a month ago, in the very same newspaper, that Johnson’s prorogation was legal. Law’s imperial armies appear to have captured Lord Sumption’s foxhole.

All of this highlights a crucial point: any discussion of technical remedies to the current constitutional challenge, be that restoring the Judicial Committee of the House of Lords or imposing statutory restraints on judicial review as Australia has done, must be accompanied, and indeed preceded, by a strong narrative counter-attack on the common-law myth of judicial infallibility.

This is not just a legal fight, and it would be foolish for champions of the political constitution to give battle on the enemy’s favoured terrain. As JAG Griffith argued in his famous 1979 essay – which anyone interested in this subject should seek out – the gravity of political power affects the law. And in a democracy, winning political power means having a compelling story to tell the voters.