Lord Faulks is a former Minister of State at the Justice Department.

The Brexit conversation may have moved onto the next stage. But the fallout from the Supreme Court’s judgment on prorogation in 2019 has left our constitution in a state of disarray.

The Conservative Party Manifesto and the Queen’s Speech make clear that the Government is serious about examining the changing constitution and restoring its balance if need be. The Supreme Court’s judgment and its wider implications are likely to be relevant to this exercise.

Distinguished legal commentators have taken different views about the Court’s decision to quash the September 2019 prorogation. Some have hailed the judgment as an historic vindication of parliamentary democracy against a rapacious, unbound executive, whereas others have decried it as an improper extension of judicial power into the heart of politics.

And some have split the difference, or at least changed their minds. Jonathan Sumption, remarkably, argued before the Supreme Court judgment that intervention would be legally improper and yet welcomed the “revolutionary” judgment that followed, apparently on the grounds that the Government was made up of fanatics (or had been acting like fanatics) and deserved a good kicking.

Policy Exchange’s Judicial Power Project has been in the vanguard of the debate, publishing a series of incisive short comments for and against the judgment, convening a high-level discussion (with Lord Sumption amongst others, which John Bald wrote about on this site) about the judgment and its implications, and contributing to the inquiry by the Public Administration and Constitutional Affairs Committee, an inquiry cut short by the general election. (One hopes that the Committee, under the leadership of its new Chair, William Wragg, will choose to revive and complete the inquiry.)

Policy Exchange also published two substantial papers taking the Supreme Court’s reasoning to task, one by Martin Loughlin of the LSE and the other by John Finnis of Oxford University. And in a new paper published by Policy Exchange today, Professor Finnis has produced what to my mind is the final word on the subject.

Why does it all matter? After all, when the Supreme Court ruled that the purported prorogation was unlawful, Parliament returned for a short period during which not very much, if anything, was achieved. And then we had a general election.

But the result of the ruling is that principled limits on the justiciability of the prerogative power to prorogue, including limits firmly imposed by Article 9 of the Bill of Rights 1689, have been set aside.

In other words, judges can now decide whether they are satisfied with the reasons (if any) the Government provides for its decision to prorogue Parliament. For many lawyers and commentators, this is an assertion of judicial power that cannot be justified by constitutional law or principle. That was also the view of the distinguished judges of the Divisional Court whose judgement was reversed by the Supreme Court without engagement with their reasoning. The decision to prorogue Parliament, however questionable it might have been, was the exercise of a clear prerogative power, the merits of which are the stuff of politics not law.

So the novelty of the Supreme Court’s judgment should not be overlooked. In his masterful new paper, which complements and completes his earlier critique, Professor Finnis explains with care just how far the Supreme Court’s judgment distorts the law of our constitution. One implication of his analysis is that the Attorney General had good reason to maintain, in the face of heated criticism in the Commons and elsewhere, that his advice that prorogation was lawful had been correct.

In the common law, how a judgment is received by lawyers often determines its relevance to the future of the law. This is doubly so in relation to a judgment that has provoked such strikingly different reactions on the part of legal commentators. Professor Finnis makes clear just how badly the Supreme Court mishandled the law of our constitution which it was duty-bound to apply and thus the damage it has done to the integrity of the UK’s political constitution. Unless his analysis can be answered, which I very much doubt, lawyers and judges should look back on the Supreme Court’s ruling as an historic mistake, a needless constitutional panic.

Unless and until the judgment is reversed by the Supreme Court or Parliament, it exposes decisions about prorogation – and by analogy decisions to seek a dissolution of Parliament or to form a government – to challenge in the courts. This may be good news for lawyers, and for those who want a second bite at the political cherry, but it constitutes a significant, unjustified constitutional shift.

What can the Government do? It can hope that the decision will simply be a one-off, and that later courts will decline to follow the judgment further. That might prove to be wishful thinking. Or it can invite Parliament to legislate to settle authoritatively the non-justiciability of the prerogative power to prorogue Parliament and perhaps also to impose further limits on the scope of that power. While they are at it, Parliament might want to legislate to protect other, related prerogative powers.

Legislation of this kind may be the only way to limit the courts’ incursion into political territory. It will almost certainly be misrepresented as some kind of “revenge” attack on the courts. Indeed, this charge has been made in anticipation of possible reform. Parliament has a constitutional responsibility to consider restoring the long-settled law of our constitution, including Article Nine of the Bill of Rights 1689, and if or when it chooses to act it will not be exacting revenge on the Supreme Court.

Indeed, it is more than a little odd to denounce legislation that would vindicate the powerful judgment of the Divisional Court – made up of the Lord Chief Justice of England and Wales, the Master of the Rolls and the President of the Queen’s Bench Division – as a populist attack on the rule of law.

Repeal of the Fixed-term Parliaments Act 2011 (a manifesto commitment) may provide an opportunity to act. (In another recent Policy Exchange paper, Stephen Laws explores further the opportunity repeal and replacement of the 2011 Act provides in this regard.)

Alternatively, the Government may choose to wait until it has the views of the Commission on the Constitution, Rights & Democracy, the remit of which appears certain to include an examination of the relationship between the legislature, the executive and the courts. For members of the commission, as for Parliamentarians in both Houses, Professor Finnis’s analysis of the Supreme Court’s missteps should be required reading.