Is the UK Supreme Court rogue to un-prorogue Parliament?

: On 24 September 2019, in a unanimous judgment the UK Supreme Court ([2019] UKSC 41) ruled that the Prime Minister’s action to prorogue (suspend) Parliament for five weeks in the run-up to the 31-10-2019 deadline of the UK leaving the European Union, was unlawful and of no effect, as it prevented Parliament from carrying out its constitutional functions without reasonable justification. Although the Court did not pronounce on the merits and demerits of Brexit, its decision delighted “Remainers” but appalled “Leavers”. The Court ruling epitomises the potency of constitutional review by an independent judiciary. The paper applies collective choice theory to analyse the ruling of the Supreme Court. This is accomplished by (a) examining the legal basis of the Court ruling; (b) reviewing arguments for judicial review and (c) exploring the effect of the Court as an additional player in the game of collective choice in a spatial decision model.

between the Executive, the Parliament and the Court and the decision to un-prorogue. Section 6 concludes.
A prorogation of parliament ends the current session of the UK Parliament. While Parliament is prorogued, neither the House of Commons (elected lower House) nor the House of Lords (unelected upper House) can meet, debate, pass legislation, or hold the executive to account, by for instance asking Ministers written or oral questions, or by meeting in committees. The Government remains in office and can exercise its powers to make secondary legislation but cannot procure the passing of Acts of Parliament or obtain approval for further spending. The decision to prorogue is a prerogative power. 2 Prerogative powers are powers recognised in common law, which are exercised by the Crown, either by the monarch or government ministers, and can be used without Parliamentary approval. The power to order prorogation lies in the monarch, acting on the advice of her government. As such, in practice, for more than a century, "the Government of the day advises the Crown to prorogue and that request is acquiesced to"

([2019] UKSC 41 [3]). 3 A short time after prorogation, a new session begins with the Queen's
Speech, which sets the legislative programme of the Government. Prorogation differs from dissolution of Parliament, which is followed by a general election to elect a new House of Commons and approve a new government. Similarly, prorogation differs from adjournment of the House (or, equivalently, the House going into recess). The latter is decided by each House passing a motion to that effect, rather than the Government. During a recess, the House does not sit but Parliamentary business can otherwise continue as usual (for example, committees may meet).

Chronicle of developments: "Events dear boy, events" 4
On 23 June 2016, the UK held an "In-Out" referendum on its European Union membership (pursuant to the European Union Referendum Act 2015); see the appendix for summary of the timeline of the events from the EU referendum to the ruling of the Supreme Court annulling the prorogation of the Parliament and the exit of the UK from the EU. With a 72.2 per cent turnout 2 For UK government prerogative powers see, for example, Bradley et al (2018). 3 Throughout the text we denote paragraph numbers of the Supreme Court judgment [2019] UKSC 41 by square brackets [.]. 4 Attributed to Harold Macmillan, UK Prime Minister, 1957-63, when asked what a prime minister fears most. of 46.5 million registered voters, 17.4 million voters voted to Leave and 16.1 million voters voted to remain, which translated into a 51.9 -48.1 per cent victory for leaving the European Union. The latter camp was split into two groups, the official "Vote Leave" Campaign headed by Conservative Ministers Michael Gove and Boris Johnson, and the "Leave.EU" Campaign headed by the Euro-sceptic MEP and the then leader of the UK Independence Party Nigel Farage (who later headed the 'Brexit' party). At the time, the "Vote Leave" group was perceived as more sympathetic to the "Soft" exit option than the latter. 5 Immediately after the referendum, David Communities Act 1972, the Act which had provided for UK's entry into what has now become the European Union, would be repealed, but much of the existing EU law as the law of the UK was to be preserved (with provision for exceptions and modifications). It stipulated that a withdrawal agreement may only be ratified if (a) the Government presents to Parliament a statement that political agreement has been reached, a copy of the negotiated withdrawal agreement and a copy of the framework for the future relationship; (b) the House of Commons has approved the withdrawal agreement and future framework; (c) the House of Lords has taken 5 A 'soft Brexit' meant a negotiated settlement out of the EU, possibly including elements of customs union and likely participation in the Single Market. A 'hard Brexit' meant withdrawing without a negotiated deal relying only on World Trade Organisation (WTO) rules implying the imposition of tariffs on at least some trade in goods between the UK and the EU. note of them both; and (d) an Act of Parliament has been passed which contains provision for the implementation of the withdrawal agreement.
Negotiations about a "smooth and orderly exit from the European Union" and a political declaration, setting out a framework for the future relationship, to be negotiated by the end of 2020, were concluded on 25th November 2018. However, the withdrawal agreement was rejected three times by the House of Commons, on 15th January 2019 (by 432 to 202 votes), on Having failed to pass the withdrawal agreement, Theresa May resigned as Prime Minister on 24th July, after the Conservative party had chosen Boris Johnson as its leader. Boris Johnson had declared that in his view the European Council will only agree to changes in the withdrawal agreement if there is a genuine risk that the United Kingdom will leave without any such agreement. He appointed Michael Gove Cabinet Office Minister to prepare for a "no deal" exit.
Yet it was also clear that a majority of the House of Commons would not support withdrawal without an agreement. On 27-28 August, acting on the advice of the Prime Minister, although conversations are not made public, the Queen proceeded to make an Order in Council 6 that would prorogue Parliament for the period 9 September -14 October.
Parliament returned from its summer recess on 3rd September, when the House of Commons passed a motion that MPs should decide for themselves (rather than the Government) what business they would transact. On 4th September they passed a bill requiring that on 19th October the Prime Minister seeks an extension of three months from the European Council, unless by then Parliament has either approved a withdrawal agreement or approved leaving without one.
On 6th September the House of Lords suspended its usual rules, so that the Bill could be passed, 6 Orders in Council are Orders that have been approved at a meeting of the Privy Council personally by the Queen. They fall into two broad categories, statutory and Prerogative. Statutory Orders are made under any of the numerous powers contained in Acts of Parliament which give Her Majesty a power to make Orders. Prerogative Orders are made under the inherent power of the Crown to act on matters for which Parliament has not legislated. See https://privycouncil.independent.gov.uk/orders/ and Bradley et al (2018). and on Monday 9 th September it received Royal Assent to become the European Union (Withdrawal) (No 2) Act 2019. The object of that Act is to prevent the United Kingdom leaving the European Union without a withdrawal agreement.
Meanwhile, on 30 July, a petition was launched by a cross-party group of 75 MPs and members of the House of Lords in the Outer House of the Court of Session of Scotland claiming that a prorogation would be unlawful and seeking a declaration to that effect and an interdict to prevent it. On 4 th September the petition was refused on the ground that the issue was non-justiciable in a court of law ([2019] CSOH 70). However, on appeal, the Inner House Court of Session, Scotland's supreme civil court, held that the advice given to the Queen was justiciable, that it was motivated by the improper purpose of stymying parliamentary scrutiny of the executive, and that it, and the prorogation which followed, were unlawful and thus null and of no effect (13 there is no doubt that the courts have jurisdiction to decide upon the existence and limits of a prerogative power. Second, the decision to advise Her Majesty to prorogue Parliament was unlawful because it had the effect of frustrating or preventing the ability of Parliament to carry out its constitutional functions without reasonable justification. It then declared that the prorogation of Parliament was likewise unlawful, null and of no effect. As our focus here is the legal case and the interactions between the executive, the legislature and the judiciary, we limit our narrative of political events at this point, even though there have been important new developments since which are still playing out (see the appendix).

3
The judgment of the Supreme Court  , in the Case of Proclamations (1611) 12 Co Rep 74, it was held that it was unlawful to alter the law by the use of the Crown's prerogative. "The King hath no prerogative, but that which the law of the land allows him", indicating that the limits of prerogative powers were set by law and were determined by the courts. Second, in Entick v Carrington (1765) 19 State Tr 1029; 2 Wils KB 275, the court declared that the Secretary of State could not order searches of private property without authority conferred by an Act of Parliament or the common law. the principle of Parliamentary sovereignty. The Court held that if there was no legal limit on the power to prorogue Parliament, then the executive could use it to "prevent Parliament from exercising its legislative authority for as long as it pleased" [42]. Consequently, the principle of Parliamentary sovereignty is incompatible with an unlimited power or prorogation. Practical constraints, such as the executive requiring Parliamentary authority to raise money to fund public services, were found to offer scant reassurance. It was nonetheless emphasised that prorogation was not in and of itself unlawful and incompatible with Parliamentary sovereignty where Parliament was prorogued for a short time such that there was only a minor effect on Parliament's ability to exercise its legislative powers. In the same way that unlimited prorogation is incompatible with Parliamentary sovereignty, so it is with Parliamentary scrutiny. Therefore, a prerogative power is limited by the constitutional principles with which it would otherwise conflict (as well as by statute and the common law) [49]. This means that "a decision to prorogue Parliament (or to advise the monarch to prorogue Parliament) will be unlawful if the prorogation has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions as a legislature and as a body responsible for the supervision of the executive" (emphasis added) [50].
The question of whether the prorogation frustrates Parliament's ability to perform its legislative function is fundamentally a question of fact for the Court to determine; then the Court must decide whether the Prime Minister's explanation for advising that Parliament should be prorogued is reasonably justified, while exercising sensitivity as to the responsibilities and experiences of the Prime Minister. In other words, the latter question is to be considered by the Court with caution.
The third question concerns whether the prorogation prevented Parliament from fulfilling its constitutional functions without reasonable justification. It was held that this prorogation prevented Parliament from carrying out its constitutional role for five out of a possible eight weeks between the end of the summer recess and the UK's exit from the European Union on 31 October. The main political parties hold their annual conferences over a three-week period in late September -early October, when the Parliament goes to recess. While it was acknowledged that such an interruption might not matter in some circumstances, the circumstances in UK politics were exceptional as "[a] fundamental change was due to take place in the Constitution of the United Kingdom on 31st October 2019. Whether or not this is a good thing is not for this or any other court to judge. The people have decided that. But that Parliament, and in particular the House of Commons as the democratically elected representatives of the people, has a right to have a voice in how that change comes about is indisputable [57]." Furthermore, the court held that no reasonable justification had been given by the government for such a long prorogation.
Accordingly, the court held that "[i]t is impossible for us to conclude, on the evidence which has been put before us, that there was any reason -let alone a good reason -to advise Her Majesty to prorogue Parliament for five weeks, from 9th or 12th September until 14th October. We cannot speculate, in the absence of further evidence, upon what such reasons might have been. It follows that the decision was unlawful" [61].
Finally, the Court examined the remedy to be granted following the decision that the advice given to the Queen to prorogue Parliament was unlawful. The Government argued that the prorogation was a "proceeding in Parliament" which cannot be challenged in court. The Court dismissed this argument; Parliament did not vote for it, the prorogation was imposed. Therefore, since the Prime Minister's advice was unlawful, it was null and of no effect. Consequently, the Order in Council, upon which the prorogation is ordered, was also unlawful and of no effect [69]. It follows that Parliament has not been prorogued. Parliament, and in particular the Speaker, decides what to do next [70].
Notwithstanding its controversial political context, the Supreme Court handed down a remarkably conservative judgment that affirms the supremacy of the UK Parliament established with the settlement of the 1688 Glorious Revolution. It upholds the traditional system of separation of powers and views its own constitutional position as one of determining "the legal limits of the powers conferred on each branch of government, and to decide whether any exercise of power has transgressed those limits. [Crucially,] the courts cannot shirk that responsibility merely on the ground that the question raised is political in tone or context" [39]. The case is an example of a situation where the Court intervenes to ensure that accountability between the branches of government is guaranteed and effective. Throughout the ruling, the Court emphasizes that the Executive is accountable to the Parliament, and there is no good reason to suspend this obligation. The Supreme Court delivered a judgment that reaffirmed Parliamentary Sovereignty as the principle at the heart of the UK Constitution, continued a tradition "of deference to Parliament", and demonstrated that it would intervene to ensure Parliament's continued supremacy. It is submitted that such a strict interpretation of the Constitution insulates the Court from criticisms of judicial activism.

Interpretation of the incomplete constitutional contract
A constitution is a form of social contract that joins the citizens of the state and defines the set of rules governing their community (Mueller 1996). Constitutions describe "property rights" to political power, that is, the powers of the different organs of state, the limits placed on them, the freedoms of the citizens and mechanisms to protect them. The case studied here concerns the division of power between different branches of the government. However, the constitution is par excellence an incomplete contract. A contract is incomplete when there is uncertainty about the rights, duties, and commitments of the contracting parties. Incompleteness originates from often enormous difficulties to perceive and describe all possible circumstances that may affect the contracting parties (what has become known as bounded rationality rather than full) and the inability of the parties to commit to the relevant actions (which makes a party vulnerable to the 8 The UK courts have long been involved in judicial review of administrative actions. But fully fledged judicial review of legislation for its compatibility with individual rights started in earnest after the 1998 passage of the Human Rights Act which empowered courts to review whether Acts of Parliament are consistent with codified rights. For a detailed analysis, see Kavanagh (2009). Ip (2014, p.223) offers details and using public choice methodology argues that the Human Rights Act was "primarily designed to maximize the partisan and corporate interests of the enacting legislative coalition." 9 Short reviews of the vast literature on independent judicial review can be found in Harnay (2005) and Tridimas (2014). Voigt (2020) offers the first and so far only textbook treatment of the field of constitutional political economy, which uses the rational choice model of economics to study the emergence of constitutions and their effects on the economic variables of interest. opportunistic tendencies of another party). Moreover, conditions change over time, as preferences and technology or random shocks disturb the prevailing equilibrium, thereby changing the interests of the parties to the agreement. Rights and obligations may then be vague and disputable. In view of such uncertainty and ambiguity, parties choose to enter what is called a "relational contract." That is, instead of agreeing to a definite and detailed plan of actions and rewards, the parties frame their relationship by agreeing on basic goals and objectives, on general provisions that are broadly applicable, on the criteria to be used in deciding what to do when unforeseen contingencies arise, on who has the power to act and the bounds limiting the range of actions that can be taken, and on dispute resolution mechanisms to be used. To overcome the incompleteness of the constitution, its signatories delegate the task of resolution of disputes, interpretation of rights, and enforcement of commitments to independent constitutional courts, grant them review powers, and agree to abide by their rulings. In a system of strong judicial review, like the US, the constitutional court can annul legislation it adjudges as incompatible with the constitution. On the other hand, in a system of weak judicial review, like the UK, the court can declare legislation incompatible with the constitutional rights, but leaves it to the legislature to remedy the legislation. Incompleteness is arguably more pronounced in the case of the Constitution of the UK which is not codified but consists of a number of treaties, laws, conventions, practices, and conforms to long established legal principles. 10

The judiciary in the principal-agent relationship
In this context, the rational choice account couches the judiciary in the architecture of the principal -agent relationship (Law 2009). A principal is an actor who lacking information or competence to take an action furthering its interests delegates authority to a knowledgeable and specialised agent to take such action. For example, the voters delegate decision making powers to their elected representatives; or the executive acts as an agent of the legislature to implement its chosen policies. In this light, three partially overlapping roles are attributed to the judiciary.
First, the judiciary, independent of the other arms of the state, may mitigate information asymmetry problems and provide authoritative answers to questions about the rules of governance contained in the constitution and the law more general. In the terminology used above, the judiciary fills the gaps left by the incomplete constitutional contract. When the judiciary interprets the constitution, it acts as a trustee of the constitution and exercises fiduciary powers . Under trusteeship, the judiciary holds all political property rights.
Second, an independent judiciary may be well placed to resolve the "strong state dilemma" (Weingast 1993) or "sorcerer's apprentice problem" (Mueller 1996), and the associated time inconsistency problems afflicting the holder of power. A state strong enough to protect the security and wealth of citizens against external or internal predators is strong enough to deprive them of their freedoms and properties and even enslave them. The following time inconsistency may then arise: A ruler may announce that he will respect private property rights so that citizens have the incentive to invest and increase output. However, when on a future date output rises, the ruler actually benefits from disrespecting property rights and confiscating the higher output. That is, the ruler has time or dynamic inconsistent preferences. Anticipating the double cross, citizens do not believe the initial promise of the ruler, refrain from investing and output stagnates. An independent judiciary with the authority to protect citizens and strike down abuses of power by government officials offers a possible solution to this problem and enhances the credibility of policy declarations (Hayo and Voigt 2007). An independent judiciary also resolves commitment problems arising when office seeking politicians pander to parochial public opinion sentiments at the expense of the long-run interest of the society, and promote policies which hurt minorities or trample upon rights. Under this circumstance, when the electorate is poorly informed, information about policy is costly to acquire and slow to emerge, granting power to a judiciary, even though it is unaccountable, may increase social welfare, because the judiciary is immune from electoral objectives (Maskin and Tirole 2004).
In the setting just described, the judiciary engages in resolving conflicts between the state and the citizens. When one considers conflict between political groups competing for office, a third role for independent judicial review emerges, that of political insurance (Landes and Posner 1975;Ramseyer (1994); Ginsburg 2002;Stephenson 2004, Hanssen 2004Tridimas 2010). When in power, different political parties wish to implement the policies conferring the highest benefits to their supporters. In so doing, they may hurt disproportionately the supporters of opposing parties.
Political parties who recognise that their hold on power is only temporary and will be in and out of office appreciate that they are better off if they and their opponents are restrained so their policies do not inflict grave losses to the opposite side. Hence, they grant independence to the judiciary, endow it with the power to strike down laws incompatible with the rules which frame the game, and abide by its rulings.
Submitting constitutional disputes to the courts introduces an additional player to the game of collective choice. The last half-century or so has witnessed a dramatic increase of submissions to both domestic and international courts to resolve political disputes of a constitutional nature, a trend which is called the "judicialization of politics (for details see among others Ferejohn 2002 and Shapiro and Stone Sweet 2002). More specifically, the constitutional court enters the collective decision game not as a decision taker who can initiate legislation, but as a veto player, whose consent is required to enact legislation. When the veto player takes a stance on a policy issue differing from the policy preferences of the agenda setters, only comparatively small changes of policy from the status quo, if at all, are enacted (Tsebelis 2002;Congleton 2011

Judicial independence
A necessary (although not sufficient) condition for judicial review is judicial independence. To resolve disputes in an unbiased way judges with the power to issue binding rulings must be protected against threats and intimidation, and stay independent of the disputants. Specifically, judicial independence means that courts enforce the law and resolve disputes without regard to the power and preferences of the parties appearing before them (La Porta et al, 2004). Judicial 11 An additional reason for endowing the judiciary with review powers is that it opens the opportunity for politicians to shift the blame for unpopular decisions to the independent national or international courts and avoid electoral defeat (Fiorina 1986). However, successful shift of responsibility for adverse policy impact requires that voters fail to see through underlying causes behind unpopular measures and remain irrational in the long-run.
independence is an imperative element of the rule of law and its beneficial consequences. 12 In general, judges are more independent, the less the government is involved in their appointment, (if relevant) the larger the legislative majorities needed for their confirmation, the longer their term of service, the smaller the risk of having their budgets reduced, the more difficult it is for the government to reverse unfavourable rulings, either by fresh legislation or by changing the charter or the composition of the judiciary (see Tridimas 2014 and the references therein).
In the UK, the Act of Settlement 1701 confirmed the independence of the judiciary and the 12 Considering judicial independence as an explanatory variable, empirical research has shown that countries with higher degrees of judicial independence enjoy higher economic performance (Henisz, 2000), greater economic and political freedom (La Porta et al. 2004), and a lower share of taxes (Tridimas, 2005). Most interestingly, Feld and Voigt (2003) distinguish between de jure independence, as described in legal texts setting up the supreme court of a country, and de facto independence which is independence of the supreme court of a country as it is actually implemented in practice. They find that only de facto judicial independence is conducive to growth; a similar result is reported by Voigt et al (2015). If, following these consultations, the Lord Chancellor is content with the recommendation made by the selection commission he forwards the person's name to the Prime Minister who, in turn, sends the recommendation to the Queen who makes the formal appointment.

A rogue agent?
Dispute resolution by the judiciary creates a new conflict. By finding in favour of one litigant and against another, the legitimacy of the court may come under attack by the loser. In order to overcome such problems courts base their rulings on generally accepted principles of justice, as expressed in formal laws and informal norms, and proclaim a normative justification for their decisions. More generally, and as highlighted by the principal-agent literature, the judiciary, as an agent with discretionary power this time, may pronounce rulings which serve its own interests instead of those of citizens and legislators (the principals). Indeed this is the usual criticism against decision making by unelected and unrepresentative judges, who often come from an elite social background. This implies the risk that independent courts may turn "rogue" and pursue deceitfully the personal and ideological interests of the judges. To safeguard against this risk a number of mechanisms have been established to secure judicial accountability, whereby accountability of an actor means that the actor is obliged to explain and justify its conduct and may be rewarded or sanctioned. Thence, the obligation of courts to publish and explain the reasons behind their decisions not only increases the information set available to all actors but also satisfies the requirement for accountability. A further constraint on the preferences of judges in judicial making is the norm of following court precedent or stare decisis (Knight and Epstein 1996).
However, a delicate balance must be struck here. If courts are held responsible for their decisions and forced to bear their costs, accountability may infringe their independence. Measures which aim to promote accountability may be abused and weaken judicial independence. 13 Impeachment is probably the most potent measure for disciplining serving judges and removing them from office, but it can also be directed against judges with views different from those of the political rulers. As a result, it is a "cumbersome, costly and visible process that exposes [legislators] to electoral danger" (Ferejohn, 1999, p.358) and is only rarely used. Less drastically, an important restriction on judicial review is the binary nature of the rulings, that is, either to enforce a policy measure introduced by the government or annul it (Tridimas 2010).
The risk of courts going rogue is mitigated when one takes into account that courts as rational actors are interested in having their rulings obeyed and accepted, and rely on the cooperation of the other two arms of the state to implement their rulings (new legislation in accordance with the court ruling must be passed, or new administrative acts must be enacted). As a result, courts have an incentive to apply a form of "auto-limitation" or self-restraint. 14 Hence, their pronouncements will tend to be inside the "core" of the preferences of the parliament and the executive, that is, the set of policy points that cannot be defeated by any other proposal. Neither the legislature nor the executive will then have an incentive to pass new legislation to overturn the decision of the court or even change the charter of the court, weakening its power.

Spatial decision equilibrium and the Supreme Court ruling
This section uses the spatial model of public choice theory to illustrate the involvement of the Supreme Court in decision making. 15 We assume a two-dimension choice space as shown in  Shapiro (2002) argues that three factors contribute to successful implementation of judicial rulings: neutrality and independence of the court from the conflicting parties; an incremental, case-bycase, mode of judicial decision making; and the technical nature of its rulings. Neutrality means that litigants recognize that the judicial decision of who wins and who loses is determined by the law rather than the judges. Incremental ruling, that is, resolution of disputes case-by-case, has two advantages. First, it facilitates decision making in an uncertain and complex environment. Second, and perhaps more importantly, it allows resolution of disputes which involve "very small immediate stakes" but pronounce principles which form the precedence which will be observed in future dispute resolution of "grand issues of politics and policy". "Case-by-case judicial decision-making is, …, a particularly good ground for easing into major policy change both by announcing big new law in small cases and by moving small doctrinal step by small doctrinal step into big changes" (p.169). The technical nature of rulings removes party politics from the judicial decision, renders court rulings as well-informed responses in an uncertain environment, and presents judges as knowledgeable specialists whose pronouncements can be trusted. 15 See Ferejohn and Weingast (1992), Hanssen (2000), Vanberg (2001), Rogers (2001), Tsebelis (2002) and Stephenson (2004). The dispute about the policy competencies of the Executive and the Parliament is resolved by the Supreme Court which clarifies the institutional setting and the legality of the actions of the other players. Specifically, the role of the Supreme Court is to interpret the constitution regarding the limits of parliamentary and executive power, but not to express preferences regarding the political issue of Brexit. The reason is that in accordance with rational choice theory, and in analogy to the other two players, the Supreme Court also has preferences about outcomes, but such preferences reflect the "deeply internalised" notions of justice held by judges, rather than political objectives. This means that, contrary to the Executive and the Parliament, the indifference curves of the Supreme Court reduce to horizontal lines. Suppose that the Court interprets the Constitution as granting power to the Parliament relative to the Executive represented by point C on the vertical axis. The Court's highest utility regarding the power of the Parliament is then represented by the indifference curve CI passing through point C. Indifference curves above and below CI indicate lower levels of utility. The Court, however, does not have agenda setting power; it only has binary choice. That is, it either enforces the position proposed by the Executive or it annuls it by confirming the status quo; it cannot impose the outcome corresponding to its highest utility. It will nevertheless pronounce in favour of the position which is closer to its highest utility point. When, as in the Figure, C lies above the midpoint M of the segment SE (EM=MS), the utility the Court derives from confirming the status quo is higher than the utility obtained from enforcing the ideal point of the Executive. Henceforth, if C lies above M, the Court annuls the prorogation. This is exactly what the UK Supreme Court ruling ordered.
With the prorogation annulled the Executive can no longer set E; equilibrium is determined by taking into account the preferences about EU participation of both the Executive and the Parliament subject to the condition that the power of the Parliament is at the level represented by the line SQ′PQ. Given its preferences regarding EU participation, the Parliament is better off on points along the segment Q′Q. With the Executive unable to establish E, forced to accept a point along SP and preferring points to the left of the status quo Q, the collective choice equilibrium will be on a point along the segment Q′P.
It is important to emphasise that the Court itself set out the test for determining the limits of executive powers to prorogue. The constitutional principles at issue limit executive prerogative power. The standard set by the Court to judge the limit is whether there was reasonable justification for suspending the Parliament for an unusually prolonged period of time. The Court held that the Executive did not offer sufficient justification. Hence, the Court is modeled as having a bliss point at C. Given that the Court established the above legal standard, the only way the Executive might have won the case was if the Court had found that the Executive had offered a reasonable justification. Had it done so, the bliss point of the Court would have been represented by a point like C′ below M. So the Court would have found for the Executive and validated the prorogation of Parliament.
It follows that the engagement of the Supreme Court in the UK collective choice game led to more UK participation than the Executive seemed to wish, thereby increasing the stability of the status quo. Very soon after the announcement of the Court ruling protestations against unelected and meddlesome judges subsided and related objections disappeared from headline news. The decision of the Supreme Court was accepted as final and the issue was closed. 17 Executive officials comply with Court rulings proclaiming their ideology for the rule of law. Nevertheless, according to the rational choice model there are additional, and arguably, stronger motives for their self-restraint. Officials who defy the Court risk the disapproval of voters, other officials and of legal professionals. They may not be able to defend their actions and careers against such a public outcry. Moreover, following the insights of principal-agent theory, both the Executive and the Parliament are the principals who voluntarily delegate to the Court resolution of constitutional disputes generating a self-enforcing equilibrium; as a result they are bound to follow its rulings.

Conclusions
The previous analysis answers the question of whether the Supreme Court was rogue with a resounding no. In sum, the Court ruled that (1) the advice given by the Prime Minister to the Queen regarding the prorogation of Parliament is a matter subject to review by the UK courts.
(2) The standards used to judge the lawfulness of the advice are the fundamental constitutional principles of parliamentary sovereignty to legislate and accountability of the executive to the parliament.
(3) The act of proroguing failed the two standards. (4) As a result of the failure, the relevant remedy is to 'un-prorogue'.
Fully consistent with the delicate trade-off between judicial independence and judicial accountability, the Court treaded carefully by not expressing an opinion about the advantages and disadvantages of the political issue of Brexit, and delivered a verdict on the limits of executive discretion and the scope of parliamentary power in the UK as it has been established by statute, practice and convention. The reason for cancelling the prorogation of the Parliament was that in the UK the Parliament is sovereign and any measure which risks this foundational element of the Constitution is null and void. A strict interpretation of the ruling is that, contrary to judicial activism, the Supreme Court has been conservative and has reaffirmed the supremacy of Parliament. It has continued a tradition of deferring to the Parliament in major policy issues.