Did the Supreme Court get Miller right?  The case was certainly one in which the judges developed, as opposed to merely applied, the law.  Even the very best lawyer could not have known for sure whether the judges would conclude that the abuse of the prerogative – and it was a very clear abuse – was so egregious the Prime Minister’s attempt to prorogue Parliament would be found to be unlawful.

Some might argue that admitting Miller developed the law is to condemn the case: judges should apply, not make, law. But the common law has been developing since its inception over 800 hundred years ago; one of the tasks of the judges is, and always has been, to improve the law.  Their law-making role is, though, distinct from that of Parliament: when judges make law they need to show that their decisions fit with past cases – they do not have a free-hand to re-write the law – and they should be slow to venture into politically controversial areas, which should normally be left to Parliament.

Though Miller has received some criticism from the press and some parliamentarians, it is far from a radical decision; it does fit with past cases.  In its willingness to subject prorogation to judicial scrutiny, it forms part of a long line of jurisprudence in which judges have steadily increased the courts’ control over the Executive’s prerogative powers, the judges recognising that there are no convincing reasons why prerogative powers should be treated any differently to statutory powers.  And in its use of broad common law principles in constitutional cases, the decision follows a trend seen in a number of recent Supreme Court decisions, including Privacy International and the first Miller decision.

But even if Miller can be squared with past case law, was the issue too politically controversial to justify judicial engagement?  Did the courts encroach on an area that should be left to the political side of the constitution?  Opponents of Miller might attempt to present this as a Brexit case, with the judges intervening to make Brexit harder to accomplish.  But Brexit was not an issue before the court: the issue was the proper balance between the Executive and Parliament, in particular, whether the Executive could shut Parliament for lengthy periods when it found Parliament’s scrutiny irksome.  The decision in Miller would have been the same regardless of the reason for the five-week prorogation; if a Corbyn Government had sought to use prorogation to push through its policies, the Supreme Court would also have intervened.   Looked at in this light, it is unsurprising that the court though it right to examine the Prime Minister’s decision.  Rather than usurping political decision-making processes, the court in Miller stepped in to preserve the functioning of those processes.  This was not a case in which the judges were second-guessing Parliament, or interfering with its operation; instead, the Supreme Court intervened to protect Parliament from a Prime Minister who is contemptuous of its constitutional position and willing to use any means to undermine its capacity to hold the Government to account.

The judgment should be seen in the broader political and constitutional context of the Johnson administration.  This prorogation, like other ploys reportedly contemplated by the Government, appears to be an attempt to play constitutional hardball, a practice that could be particularly damaging in a constitutional system like the UK’s which is grounded in conventions and understandings. It is hardly surprising that the Supreme Court, in the face of the Prime Minister’s brazen disregard for the constitution, has developed the law to protect Parliament.  We can expect similar rulings from the Supreme Court if any other dubious constitutional ideas floating around Downing Street are put into action.

Nick Barber is Professor of Constitutional Law and Theory, University of Oxford