This post was contributed by Colin Munro, Emeritus Professor of Constitutional Law, University of Edinburgh and tutor for Undergraduate Laws.
The referendum on EU membership held in 2016 has been followed by a long period of turbulence in domestic politics that has tested constitutional arrangements in a variety of ways. For students of public law, it needs to be remembered that, since June 2017, there has been a minority government in office. Minority government in Britain is relatively abnormal but, when it obtains, accounts of the operation of government and Parliament in normal times need to be qualified because the constitutional dynamic between the two is significantly altered. Throw in to the mix a House of Commons Speaker who is prepared to push the envelope and (since July 2019) a Prime Minister who became party leader on a platform of “do or die” over Brexit, and the mixture is combustible indeed.
It was perhaps inevitable that the courts would become one of the arenas for protagonists, as has already been seen in R (Miller) v Secretary of State for Exiting the EU  UKSC 5 and Wightman and Others v Secretary of State for Exiting the EU Case C-621/18. Now we have R(Miller) v The Prime Minister, Cherry v Advocate General for Scotland  UKSC 41. On appeals from the English High Court and the Scottish Court of Session, heard together, the Supreme Court had to consider the lawfulness of the Government’s attempted prorogation or suspension of Parliament from 10th September until 14th October, a period of five weeks that would occupy a large portion of the time available ahead of the UK’s scheduled departure from the EU. Prorogations in recent times have usually (but not invariably) been for periods of about one week, but the House of Commons itself has normally agreed to recess adjournments, usually amounting to about three weeks in September to allow for the main party conferences to take place. The Government argued that the effective difference from what normally occurred was quite small, and there would still be ample time for discussion of Brexit business. As it proved, there was sufficient time in the few days between the seeking of authority for prorogation and the start of the suspension period for majorities in the two Houses to approve, against the wishes of the Government, what became the European Union (Withdrawal) (No. 2) Act 2019 and seeks to mandate the Prime Minister to ask EU states for a further extension, failing approval of a withdrawal agreement in October.
Prorogation is a royal prerogative power, authorised by an Order in Council from the Privy Council. By convention, the Sovereign acts on the advice of the Prime Minister in this regard. The litigants, principally Mrs Gina Miller in England and a group of politicians headed by the SNP MP Joanna Cherry in Scotland, were challenging the lawfulness of the Prime Minister’s advice, from which the consequent actions that led to the suspension of Parliament on 10th September, had derived.
The Supreme Court, sitting with the maximum of 11 judges, heard the case as a matter of urgency, and published its decision on 24th September. The court held unanimously that the advice had been unlawful, rendering the Order in Council and the purported prorogation null and void in consequence. Accordingly the Houses reconvened on 25th September, with the two week hiatus redesignated as an adjournment.
For the court, the first question to be answered was whether the lawfulness of the advice was a justiciable matter, it being the first occasion on which this had been tested. It was already well established that the courts had jurisdiction to adjudicate on the existence and extent of prerogatives, as shown by the Case of Proclamations (1611) 12 Co Rep 74. As distinct from that, issues concerning the manner of exercise, following the decision of the House of Lords in Council of Civil Service Unions  AC 374 were reviewable in principle, but depending on the nature and subject matter involved. Some issues have been categorised as questions of “high policy” or as being “political questions”, for example, and treated as non-justiciable.
On this crucial question, the Supreme Court diverged from the view taken by the High Court. A strong Divisional Court (Lord Burnett LCJ, Sir Terence Etherton MR and Dame Victoria Sharp PQBD) had dismissed the challenge as involving a “political” issue that was non-justiciable, given what they viewed as an absence of legal standards by which to assess the legality of the executive’s actions:  EWHC 2381.
The Supreme Court evaded that difficulty by classifying the instant case as being about the scope or limits of the prerogative power rather than about the manner of its exercise. They also found standards by which to assess the lawfulness of the advice, out of what they described as the numerous constitutional principles that exist in our uncodified constitution [paras 39, 40]. Two such principles were relevant for this case. The first of these was parliamentary sovereignty, which in their view was a foundational principle, the effect of which was not confined to recognition of Acts of Parliament as the highest form of law. The second principle relied on was parliamentary accountability, by which the Government is politically answerable to the Houses of Parliament. These principles, the court suggested, would be undermined or jeopardised if an unreasonably long prorogation frustrated or restricted the ability of Parliament to carry out its constitutional functions. The Inner House of the Court of Session had held the Prime Minister’s advice to be unlawful because, they concluded, it was motivated by the improper purpose of stymieing parliamentary scrutiny of the Government:  CSIH 49. The Supreme Court, however, avoided reaching any conclusion on purpose by concentrating instead on effect.
In the court’s view, the Prime Minister’s action “of course” had the effect of frustrating or preventing Parliament from carrying out its constitutional role for a critical period [55,56], and the action was therefore unlawful unless there was a reasonable justification. From the sparse documentation disclosed to the court, it was impossible to conclude “that there was any reason – let alone a good reason” for a prorogation of such length to take place in the circumstances . In notably clear and simple language, Lady Hale and her ten colleagues had ruled as unlawful the Prime Minister’s advice to the Queen on the matter.
Here are a few questions to think about over the next few days. My responses will form part of a linked blog post which will be published shortly.
Was this case about Brexit?
Was this case about constitutional conventions?
Did the case involve parliamentary sovereignty?
Did the case involve the rule of law?
Did the separation of powers feature?
Do we learn anything about the royal prerogative from this case?
Where does the case leave the prerogative of prorogation?
Should the case have been dismissed by reason of parliamentary privilege?
Was this a landmark case?