The Brexit case – implications for Australia

10 January 2020
Lionel Hogg, Partner, Brisbane

Amidst the Brexit debacle, the UK Supreme Court[1] has invented a brand-new rule limiting executive power. Yet, the core legal principles supporting this politically controversial development are thoroughly orthodox and, despite different constitutional arrangements, may strongly influence how executive power is exercised under Australian law.


The Supreme Court was asked to determine whether the Prime Minister’s advice to the Queen, that Parliament should be prorogued for about 5 weeks amidst political manoeuvring on the terms of the United Kingdom’s departure from the European Union, was lawful.

The conventional wisdom, prior to the decision, was that a decision of the Prime Minister to advise the Queen to prorogue Parliament was not justiciable. Rather, it was a political decision. Parliament could be prorogued for various reasons, including to gain legislative or political advantage.[2] Instead of the Prime Minister’s advice being reviewable by the courts, the Prime Minister is accountable only to Parliament; the courts should not enter the political arena but should respect the separation of powers and defer to the political decision.

Conventions of deference function acceptably when those exercising powers do so conventionally. When the executive, for collateral purposes, attempts to subvert a process formed by convention, the common law has a unique capacity to restore legitimacy by realigning the process with its inherent purpose.


The Supreme Court concluded that, as a necessary implication of parliamentary sovereignty, the Prime Minister’s advice to Her Majesty was unlawful, void and of no effect.

Whether the exercise of the prerogative was open to judicial review, the existence and limits of the prerogative were matters properly determined by the court.

[Every] prerogative power has its limits, and it is the function of the court to determine, when necessary, where they lie.[3]

In doing so, the court invented a new test limiting executive power and offered an expansive analysis of the principles of parliamentary sovereignty and accountability.

The new test is a matter of some political controversy because its method of formulation necessarily appropriates to the court the right to review the executive action. The analysis of constitutional principles, however, is both more orthodox and potentially more significant for future developments, including in Australia.

New test

The court articulated a new standard to determine the limit upon the executive power to prorogue.

[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 the body responsible for the supervision of the executive. In such a situation, the court will intervene if the effect is sufficiently serious to justify such an exceptional course.[4]

The new standard is “not concerned with the mode of exercise of the prerogative power within its lawful limits” but rather is “a standard which determines the limits of the power” and therefore is, by definition, justiciable.[5]

This is a clever distinction without a functional difference, of course. However, defining a power by reference to the effect of its exercise is not uncommon; the extent of most rights and freedoms is usually limited by reference to their exercise.

The requirement on the executive to offer “reasonable justification” is considerably stricter than the traditional Wednesbury[6] standard and may also be a source of criticism. However, the court did note that “the Government must be accorded a great deal of latitude in making decisions of this nature”.[7] And, on the facts, the government offered no reasons (“let alone a good reason”)[8] for proroguing, presumably for the perceived procedural advantage of avoiding cross-examination as to motive.

Parliamentary sovereignty

The new test upholds parliamentary sovereignty by freshly articulating the complex interrelationship of parliament and the executive within the constitutional system.

In doing so by reference to fundamental principles, it clarifies the boundaries of responsibility for each branch of government (by better articulating the interdependent functions of the participants) and expands the application of principles of legality beyond the confines of statutory interpretation. In each respect, these developments may influence Australian law.

The analysis of parliamentary sovereignty is entirely orthodox.

[Laws] enacted by the Crown in Parliament are the supreme form of law in our legal system, with which everyone, including the Government, must comply.[9]

The court proceeded to unpack some of the natural implications of that orthodox position, including some prior examples,[10] before finding another principle raised by this case.

The sovereignty of Parliament would, however, be undermined as the foundational principle of our constitution if the executive could, through the use of the prerogative, prevent Parliament from exercising its legislative authority for as long as it pleased.[11]

This conclusion, from orthodox roots, means that the court’s restraint of an abuse of executive power in this case reinforces, rather than undermines, the separation of powers.

Most fascinating is the definition of the limits of the power to prorogue by reference to the effect of the decision to prorogue. In this case, the power to prorogue arose from prerogative, not statute. Despite this, the court elected to limit the power by reference to the (clear) principles of legality that would attend it were it a statutory power, holding that the principles of legality extend to prerogative powers.[12] Although the facts of Miller & Cherry are quite exceptional, the expansion of principles of legality may have wider implications.

Implications in Australia

The United Kingdom has an unwritten constitution, unlike Australia. This does not mean that Miller & Cherry is of no relevance.

In Australia, the Convention Debates and the terms of the Constitution itself make it clear that the Constitution intended to provide for the institutions of representative and responsible government, including a system of responsible ministerial government.[13] Within the structure and text of the Constitution the High Court has found an implied freedom of political communication, restricting legislative powers by necessary implication to preserve and protect that system.[14]

Miller & Cherry demonstrates that there may be other spheres of activity – legislative or executive action – that from time to time are found to be incompatible with the maintenance of the system. The express rationale for the implied freedom cases in Australia provides foundation for other legal restrictions necessary to preserve the integrity of the system.[15] There is good reason to think that the Miller & Cherry approach on sovereignty and accountability would be adopted in Australia within the text and structure of our written constitution. Whether the limits of the power would be demarcated in the same way is an open question.[16]

On the principles of legality, the High Court has been adamant that they are rules of statutory interpretation.[17] The inexorable logic of the forensic systemic analysis undertaken by the Supreme Court may force the High Court at least to reflect on the justification for confining principles of legality in this way. If the system dictates a scaffolding of proper inter-relationships and conduct as the security of its institutional integrity, why should principles of legality (even if not causes of action) be confined to correcting exercises of statutory power but not others?

Even if the High Court were to reconsider principles of legality, it likely would not be in a Miller & Cherry scenario. In Australia, the power to prorogue Parliament is constitutional, rather than a prerogative power, at both a federal[18] and state[19] level. The issue of its application beyond statutory interpretation would not arise.

Key takeaway

The Supreme Court’s insistence on restating the institutional structures on which the democratic system are founded is a useful and welcome development. Although Australia’s constitutional arrangements differ from those in the United Kingdom, there is good reason to think that the Miller & Cherry approach on sovereignty and accountability would be adopted in Australia. The approach of the Supreme Court to broader questions surely will also influence future cases in Australia, particularly in times when institutional integrity is tested.

[1] R (on the application of Miller) v The Prime Minister; Cherry and others v Advocate General for Scotland [2019] UKSC 41
[2] See the decision of the Divisional Court in R (on the application of Miller) v The Prime Minister and others [2019] EWHC 2381 (QB) [55]
[3] Miller & Cherry n1 [38]
[4] Miller & Cherry n1 [50]
[5] Miller & Cherry n1 [52]
[6] Associated Provincial Picture Houses Ltd v Wednesbury Corporation (1948) 1 KB 223
[7] Miller & Cherry n1 [58]
[8] Miller & Cherry n1 [61]
[9] Miller & Cherry n1 [41]. Ms Miller’s argument was that the Prime Minister is subordinate to Parliament and must account to Parliament. Although the Prime Minister is accountable to Parliament, he (or she) must account in accordance with the rule of law, which the courts have a constitutional duty to determine and enforce.
[10] Such as that prerogative powers may not be used incompatibly with legislation (Case of Proclamations (1611) 12 Co Rep 74): Miller & Cherry n1 [41]
[11] Miller & Cherry n1 [42]. An unlimited power of prorogation would therefore be incompatible with the legal principle of Parliamentary sovereignty.
[12] Miller & Cherry n1 [40]. “Since the power is recognised by the common law, and has to be compatible with common law principles, those principles may illuminate where its boundaries lie. In particular, the boundaries of a prerogative power relating to the operation of Parliament are likely to be illuminated, and indeed determined, by the fundamental principles of our constitutional law.” [38]
[13] The executive power is expressly vested in the Queen and exercisable by the Governor-General. It is exercised on the initiative and advice of Ministers.
[14] Lange v Australian Broadcasting Corporation (1997) 189 CLR 520
[15] For example, in Lange (n 14) the court noted that constitutional provisions which prescribe the system of responsible government necessarily imply a limitation on legislative and executive power to deny the electors and their representatives information concerning the conduct of the executive branch of government throughout the life of a federal Parliament
[16] The Supreme Court in Miller & Cherry invented a new threshold of “reasonable justification”. The High Court implied freedom cases require a “materially unjustified effect” [Comcare v Banerji [2019] HCA 23 [20] (Kiefel CJ, Bell, Keane, Nettle JJ)] determined by proportionality testing.
[17] There are many cases reinforcing this, starting with Potter v Minahan (1908) 7 CLR 277 and Melbourne Corporation v Barry (1922) 31 CLR 174 and extending to a large number of 21st century decisions.
[18] Constitution, s5
[19] Constitution of Queensland 2001 s15(2); Constitution Act 1902 (NSW) s10A; Constitution Act 1975 (Vic) s8(2); Constitution Act 1889 (WA) s3; Constitution Act 1934 (SA) s6(1); Constitution Act 1934 (Tas) s12(2)


Authored by:

Lionel Hogg, Partner

This update does not constitute legal advice and should not be relied upon as such. It is intended only to provide a summary and general overview on matters of interest and it is not intended to be comprehensive. You should seek legal or other professional advice before acting or relying on any of the content.

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