The essentials of the UK Supreme Court’s decision on the important topic of whether the UK Government needed Parliamentary approval before triggering Article 50. The Supreme Court decided that it did.




  1. On 1 January 1973, the United Kingdom became a member of the European Economic Community (“the EEC”) and certain other associated European organisations. On that date, EEC law took effect as part of the domestic law of the United Kingdom, in accordance with the European Communities Act 1972 which had been passed ten weeks earlier. Over the next 40 years, the EEC expanded from nine to 28 member states, extended its powers or “competences”, merged with the associated organisations, and changed its name to the European Community in 1993 and to the European Union in 2009.
  2. In December 2015, the UK Parliament passed the European Union Referendum Act, and the ensuing referendum on 23 June 2016 produced a majority in favour of leaving the European Union. UK government ministers (whom we will call “ministers” or “the UK government”) thereafter announced that they would bring UK membership of the European Union to an end. The question before this Court concerns the steps which are required as a matter of UK domestic law before the process of leaving the European Union can be initiated. The particular issue is whether a formal notice of withdrawal can lawfully be given by ministers without prior legislation passed in both Houses of Parliament and assented to by HM The Queen.
  3. It is worth emphasising that nobody has suggested that this is an inappropriate issue for the courts to determine. It is also worth emphasising that this case has nothing to do with issues such as the wisdom of the decision to withdraw from the European Union, the terms of withdrawal, the timetable or arrangements for withdrawal, or the details of any future relationship with the European Union. Those are all political issues which are matters for ministers and Parliament to resolve. They are not issues which are appropriate for resolution by judges, whose duty is to decide issues of law which are brought before them by individuals and entities exercising their rights of access to the courts in a democratic society.
  4. Some of the most important issues of law which judges have to decide concern questions relating to the constitutional arrangements of the United Kingdom. These proceedings raise such issues. As already indicated, this is not because they concern the United Kingdom’s membership of the European Union; it is because they concern (i) the extent of ministers’ power to effect changes in domestic law through exercise of their prerogative powers at the international level, and (ii) the relationship between the UK government and Parliament on the one hand and the devolved legislatures and administrations of Scotland, Wales and Northern Ireland on the other.
  5. The main issue on this appeal concerns the ability of ministers to bring about changes in domestic law by exercising their powers at the international level, and it arises from two features of the United Kingdom’s constitutional arrangements. The first is that ministers generally enjoy a power freely to enter into and to terminate treaties without recourse to Parliament. This prerogative power is said by the Secretary of State for Exiting the European Union to include the right to withdraw from the treaties which govern UK membership of the European Union (“the EU Treaties”). The second feature is that ministers are not normally entitled to exercise any power they might otherwise have if it results in a change in UK domestic law, unless statute, ie an Act of Parliament, so provides. The argument against the Secretary of State is that this principle prevents ministers withdrawing from the EU Treaties, until effectively authorised to do so by a statute.

The main issue: the 1972 Act and prerogative powers

Summary of the arguments on the main issue

  1. The Secretary of State’s case is based on the existence of the well-established prerogative powers of the Crown to enter into and to withdraw from treaties. He contends that ministers are entitled to exercise this power in relation to the EU Treaties, and therefore to give Notice without the need for any prior legislation. Following the giving of Notice by the end of March 2017, ministers intend that a “Great Repeal Bill” will be laid before Parliament. This will repeal the 1972 Act and, wherever practical, it will convert existing EU law into domestic law at least for a transitional period. Under article 50, withdrawal will occur not more than two years after the Notice is given (unless that period is extended by unanimous agreement among the other member states), and it is intended that the Great Repeal Bill will come into force at that point.
  2. The applicants’ case in that connection is that when Notice is given, the United Kingdom will have embarked on an irreversible course that will lead to much of EU law ceasing to have effect in the United Kingdom, whether or not Parliament repeals the 1972 Act. As Lord Pannick QC put it for Mrs Miller, when ministers give Notice they will be “pulling … the trigger which causes the bullet to be fired, with the consequence that the bullet will hit the target and the Treaties will cease to apply”. In particular, he said, some of the legal rights which the applicants enjoy under EU law will come to an end. This, he submitted, means that the giving of Notice would pre-empt the decision of Parliament on the Great Repeal Bill. It would be tantamount to altering the law by ministerial action, or executive decision, without prior legislation, and that would not be in accordance with our law.

The constitutional background

40        Unlike most countries, the United Kingdom does not have a constitution in the sense of a single coherent code of fundamental law which prevails over all other sources of law. Our constitutional arrangements have developed over time in a pragmatic as much as in a principled way, through a combination of statutes, events, conventions, academic writings and judicial decisions. Reflecting its development and its contents, the UK constitution was described by the constitutional scholar, Professor AV Dicey, as “the most flexible polity in existence” – Introduction to the Study of the Law of the Constitution (8th ed, 1915), p 87.

  1. Originally, sovereignty was concentrated in the Crown, subject to limitations which were ill-defined and which changed with practical exigencies. Accordingly, the Crown largely exercised all the powers of the state (although it appears that even in the 11th century the King rarely attended meetings of his Council, albeit that its membership was at his discretion). However, over the centuries, those prerogative powers, collectively known as the Royal prerogative, were progressively reduced as Parliamentary democracy and the rule of law developed. By the end of the 20th century, the great majority of what had previously been prerogative powers, at least in relation to domestic matters, had become vested in the three principal organs of the state, the legislature (the two Houses of Parliament), the executive (ministers and the government more generally) and the judiciary (the judges). It is possible to identify a number of seminal events in this history, but a series of statutes enacted in the twenty years between 1688 and 1707 were of particular legal importance. Those statutes were the Bill of Rights 1688/9 and the Act of Settlement 1701 in England and Wales, the Claim of Right 1689 in Scotland, and the Acts of Union 1706 and 1707 in England and Wales and in Scotland respectively. (Northern Ireland joined the United Kingdom pursuant to the Acts of Union 1800 in Britain and Ireland).
  2. The independence of the judiciary was formally recognised in these statutes. In the broadest sense, the role of the judiciary is to uphold and further the rule of law; more particularly, judges impartially identify and apply the law in every case brought before the courts. That is why and how these proceedings are being decided. The law is made in or under statutes, but there are areas where the law has long been laid down and developed by judges themselves: that is the common law. However, it is not open to judges to apply or develop the common law in a way which is inconsistent with the law as laid down in or under statutes, ie by Acts of Parliament.
  3. This is because Parliamentary sovereignty is a fundamental principle of the UK constitution, as was conclusively established in the statutes referred to in para 41 above. It was famously summarised by Professor Dicey as meaning that Parliament has “the right to make or unmake any law whatsoever; and further, no person or body is recognised by the law as having a right to override or set aside the legislation of Parliament” – op cit, p 38. The legislative power of the Crown is today exercisable only through Parliament. This power is initiated by the laying of a Bill containing a proposed law before Parliament, and the Bill can only become a statute if it is passed (often with amendments) by Parliament (which normally but not always means both Houses of Parliament) and is then formally assented to by HM The Queen. Thus, Parliament, or more precisely the Crown in Parliament, lays down the law through statutes – or primary legislation as it is also known – and not in any other way.
  4. In the early 17th century Case of Proclamations (1611) 12 Co Rep 74, Sir Edward Coke CJ said that “the King by his proclamation or other ways cannot change any part of the common law, or statute law, or the customs of the realm”. Although this statement may have been controversial at the time, it had become firmly established by the end of that century. In England and Wales, the Bill of Rights 1688 confirmed that

“the pretended power of suspending of laws or the execution of laws by regall authority without consent of Parlyament is illegall” and that “the pretended power of dispensing with laws or the execution of laws by regall authoritie as it hath beene assumed and exercised of late is illegall”…

  1. The Crown’s administrative powers are now exercised by the executive, ie by ministers who are answerable to the UK Parliament. However, consistently with the principles established in the 17th century, the exercise of those powers must be compatible with legislation and the common law. Otherwise, ministers would be changing (or infringing) the law, which, as just explained, they cannot do. A classic statement of the position was given by Lord Parker of Waddington in The Zamora [1916] 2 AC 77, 90:

“The idea that the King in Council, or indeed any branch of the Executive, has power to prescribe or alter the law to be administered by Courts of law in this country is out of harmony with the principles of our Constitution. It is true that, under a number of modern statutes, various branches of the Executive have power to make rules having the force of statutes, but all such rules derive their validity from the statute which creates the power, and not from the executive body by which they are made. No one would contend that the prerogative involves any power to prescribe or alter the law administered in Courts of Common Law or Equity.”

  1. It is true that ministers can make laws by issuing regulations and the like, often known as secondary or delegated legislation, but (save in limited areas where a prerogative power survives domestically, as exemplified by the cases mentioned in paras 52 and 53 below) they can do so only if authorised by statute. So, if the regulations are not so authorised, they will be invalid, even if they have been approved by resolutions of both Houses under the provisions of the relevant enabling Act – for a recent example see R (The Public Law Project) v Lord Chancellor [2016] AC 1531.

The Royal prerogative and Treaties

  1. The Royal prerogative encompasses the residue of powers which remain vested in the Crown, and they are exercisable by ministers, provided that the exercise is consistent with Parliamentary legislation. In Burmah Oil Co (Burma Trading) Ltd v Lord Advocate [1965] AC 75, 101, Lord Reid explained that the Royal prerogative is a source of power which is “only available for a case not covered by statute”. Professor HWR Wade summarised the position in his introduction to the first edition of what is now Wade and Forsyth on Administrative Law (1961), p 13:

“[T]he residual prerogative is now confined to such matters as summoning and dissolving Parliament, declaring war and peace, regulating the armed forces in some respects, governing certain colonial territories, making treaties (though as such they cannot affect the rights of subjects), and conferring honours. The one drastic internal power of an administrative kind is the power to intern enemy aliens in time of war.”

  1. Thus, consistently with Parliamentary sovereignty, a prerogative power however well-established may be curtailed or abrogated by statute. Indeed, as Professor Wade explained, most of the powers which made up the Royal prerogative have been curtailed or abrogated in this way. The statutory curtailment or abrogation may be by express words or, as has been more common, by necessary implication. It is inherent in its residual nature that a prerogative power will be displaced in a field which becomes occupied by a corresponding power conferred or regulated by statute. This is what happened in the two leading 20th century cases on the topic, Attorney General v De Keyser’s Royal Hotel Ltd [1920] AC 508 and Fire Brigades Union cited above. As Lord Parmoor explained in De Keyser at p 575, when discussing the prerogative power to take a subject’s property in time of war:

“The constitutional principle is that when the power of the Executive to interfere with the property or liberty of subjects has been placed under Parliamentary control, and directly regulated by statute, the Executive no longer derives its authority from the Royal Prerogative of the Crown but from Parliament, and that in exercising such authority the Executive is bound to observe the restrictions which Parliament has imposed in favour of the subject.”

  1. In Burmah Oil cited above, at p 101, Lord Reid described prerogative powers as a “relic of a past age”, but that description should not be understood as implying that the Royal prerogative is either anomalous or anachronistic. There are important areas of governmental activity which, today as in the past, are essential to the effective operation of the state and which are not covered, or at least not completely covered, by statute. Some of them, such as the conduct of diplomacy and war, are by their very nature at least normally best reserved to ministers just as much in modern times as in the past, as indeed Lord Reid himself recognised in Burmah Oil at p 100.

50        … it is a fundamental principle of the UK constitution that, unless primary legislation permits it, the Royal prerogative does not enable ministers to change statute law or common law. As Lord Hoffmann observed in R (Bancoult) v Secretary of State for Foreign and Commonwealth Affairs (No 2) [2009] AC 453, para 44, “since the 17th century the prerogative has not empowered the Crown to change English common or statute law”…. Exercise of ministers’ prerogative powers must therefore be consistent both with the common law as laid down by the courts and with statutes as enacted by Parliament.

  1. Further, ministers cannot frustrate the purpose of a statute or a statutory provision, for example by emptying it of content or preventing its effectual operation…
  2. The fact that the exercise of prerogative powers cannot change the domestic law does not mean that such an exercise is always devoid of domestic legal consequences. There are two categories of case where exercise of the prerogative can have such consequences. The first is where it is inherent in the prerogative power that its exercise will affect the legal rights or duties of others. Thus, the Crown has a prerogative power to decide on the terms of service of its servants, and it is inherent in that power that the Crown can alter those terms so as to remove rights, albeit that such a power is susceptible to judicial review…The Crown also has a prerogative power to destroy property in wartime in the interests of national defence (although at common law compensation was payable: Burmah Oil cited above). While the exercise of the prerogative power in such cases may affect individual rights, the important point is that it does not change the law, because the law has always authorised the exercise of the power.
  3. The second category comprises cases where the effect of an exercise of prerogative powers is to change the facts to which the law applies. Thus, the exercise of the prerogative to declare war will have significant legal consequences: actions which were previously lawful may become treasonable…. These are examples where the exercise of the prerogative power alters the status of a person, thing or activity so that an existing rule of law comes to apply to it. However, in such cases the exercise has not created or changed the law, merely the extent of its application.
  4. The most significant area in which ministers exercise the Royal prerogative is the conduct of the United Kingdom’s foreign affairs. This includes diplomatic relations, the deployment of armed forces abroad, and, particularly in point for present purposes, the making of treaties. There is little case law on the power to terminate or withdraw from treaties, but, as a matter of both logic and practical necessity, it must be part of the treaty-making prerogative. As Lord Templeman put it in JH Rayner (Mincing Lane) Ltd v Department of Trade and Industry [1990] 2 AC 418, 476, “[t]he Government may negotiate, conclude, construe, observe, breach, repudiate or terminate a treaty”.
  5. Subject to any restrictions imposed by primary legislation, the general rule is that the power to make or unmake treaties is exercisable without legislative authority and that the exercise of that power is not reviewable by the courts – …Lord Coleridge CJ said that the Queen acts “throughout the making of the treaty and in relation to each and every of its stipulations in her sovereign character, and by her own inherent authority” – Rustomjee v The Queen (1876) 2 QBD 69, 74. This principle rests on the so-called dualist theory, which is based on the proposition that international law and domestic law operate in independent spheres. The prerogative power to make treaties depends on two related propositions. The first is that treaties between sovereign states have effect in international law and are not governed by the domestic law of any state… The second proposition is that, although they are binding on the United Kingdom in international law, treaties are not part of UK law and give rise to no legal rights or obligations in domestic law.
  6. It is only on the basis of these two propositions that the exercise of the prerogative power to make and unmake treaties is consistent with the rule that ministers cannot alter UK domestic law. Thus, in Higgs v Minister of National Security [2000] 2 AC 228, 241, Lord Hoffmann pointed out that the fact that treaties are not part of domestic law was the “corollary” of the Crown’s treaty-making power. In JH Rayner cited above, at p 500, Lord Oliver of Aylmerton put it thus:

“As a matter of the constitutional law of the United Kingdom, the Royal Prerogative, whilst it embraces the making of treaties, does not extend to altering the law or conferring rights upon individuals or depriving individuals of rights which they enjoy in domestic law without the intervention of Parliament. Treaties, as it is sometimes expressed, are not self-executing. Quite simply, a treaty is not part of English law unless and until it has been incorporated into the law by legislation. So far as individuals are concerned, it is res inter alios acta [ie something done between others], from which they cannot derive rights and by which they cannot be deprived of rights or subjected to obligations; and it is outside the purview of the court not only because it is made in the conduct of foreign relations, which are a prerogative of the Crown, but also because, as a source of rights and obligations, it is irrelevant.”

  1. It can thus fairly be said that the dualist system is a necessary corollary of Parliamentary sovereignty, or, to put the point another way, it exists to protect Parliament not ministers. Professor Campbell McLachlan in Foreign Relations Law (2014), para 5.20, neatly summarises the position in the following way:


“If treaties have no effect within domestic law, Parliament’s legislative supremacy within its own polity is secure. If the executive must always seek the sanction of Parliament in the event that a proposed action on the international plane will require domestic implementation, parliamentary sovereignty is reinforced at the very point at which the legislative power is engaged.”

  1. While ministers have in principle an unfettered power to make treaties which do not change domestic law, it had become fairly standard practice by the late 19th century for treaties to be laid before both Houses of Parliament at least 21 days before they were ratified, to enable Parliamentary objections to be heard. In 1924, following an indication by the previous government that it did not regard itself as bound by the practice, Arthur Ponsonby, the Parliamentary Under-Secretary of State for Foreign Affairs, assured the House of Commons that ministers would in future adhere to this practice, which became known as the Ponsonby Convention. The convention was superseded and formalised by section 20 of the Constitutional Reform and Governance Act 2010. However, by virtue of section 23(1) of that Act, this section does not apply to new EU Treaties, because they are governed by the more specific statutory controls discussed in paras 28 and 29 above.
  2. With that background, we turn to analyse the effect of the 1972 Act and the arguments as to whether, in the absence of prior authority from Parliament in the form of a statute, the giving of Notice by ministers would be ineffective under the United Kingdom’s constitutional requirements, as it would otherwise impermissibly result in a change in domestic law.

The status and character of the 1972 Act

  1. Many statutes give effect to treaties by prescribing the content of domestic law in the areas covered by them. The 1972 Act does this, but it does considerably more as well. It authorises a dynamic process by which, without further primary legislation (and, in some cases, even without any domestic legislation), EU law not only becomes a source of UK law, but actually takes precedence over all domestic sources of UK law, including statutes. This may sound rather dry or technical to many people, but in constitutional terms the effect of the 1972 Act was unprecedented. Indeed, it is fair to say that the legal consequences of the United Kingdom’s accession to the EEC were not fully appreciated by many lawyers until the Factortame litigation in the 1990s – see the House of Lords decisions in R v Secretary of State for Transport, Ex p Factortame Ltd (No 2) [1991] 1 AC 603 and (No 5) [2000] 1 AC 524. Of course, consistently with the principle of Parliamentary sovereignty, this unprecedented state of affairs will only last so long as Parliament wishes: the 1972 Act can be repealed like any other statute. For that reason, we would not accept that the so-called fundamental rule of recognition (ie the fundamental rule by reference to which all other rules are validated) underlying UK laws has been varied by the 1972 Act or would be varied by its repeal.
  2. In one sense, of course, it can be said that the 1972 Act is the source of EU law, in that, without that Act, EU law would have no domestic status. But in a more fundamental sense and, we consider, a more realistic sense, where EU law applies in the United Kingdom, it is the EU institutions which are the relevant source of that law. The legislative institutions of the EU can create or abrogate rules of law which will then apply domestically, without the specific sanction of any UK institution… It is also true that EU law enjoys its automatic and overriding effect only by virtue of the 1972 Act, and thus only while it remains in force. That point simply reflects the fact that Parliament was and remains sovereign: so, no new source of law could come into existence without Parliamentary sanction – and without being susceptible to being abrogated by Parliament. However, that in no way undermines our view that it is unrealistic to deny that, so long as that Act remains in force, the EU Treaties, EU legislation and the interpretations placed on these instruments by the Court of Justice are direct sources of UK law.
  3. The 1972 Act did two things which are relevant to these appeals. First, it provided that rights, duties and rules derived from EU law should apply in the United Kingdom as part of its domestic law. Secondly, it provided for a new constitutional process for making law in the United Kingdom. These things are closely related, but they are legally and conceptually distinct. The content of the rights, duties and rules introduced into our domestic law as a result of the 1972 Act is exclusively a question of EU law. However, the constitutional processes by which the law of the United Kingdom is made is exclusively a question of domestic law.
  4. Under the terms of the 1972 Act, EU law may take effect as part of the law of the United Kingdom in one of three ways. First, the EU Treaties themselves are directly applicable by virtue of section 2(1). Some of the provisions of those Treaties create rights (and duties) which are directly applicable in the sense that they are enforceable in UK courts. Secondly, where the effect of the EU Treaties is that EU legislation is directly applicable in domestic law, section 2(1) provides that it is to have direct effect in the United Kingdom without the need for further domestic legislation. This applies to EU Regulations (which are directly applicable by virtue of article 288 of the TFEU). Thirdly, section 2(2) authorises the implementation of EU law by delegated legislation. This applies mainly to EU Directives, which are not, in general, directly applicable but are required (again by article 288) to be transposed into national law. While this is an international law obligation, failure of the United Kingdom to comply with it is justiciable in domestic courts, and some Directives may be enforced by individuals directly against national governments in domestic courts. Further, any serious breach by the UK Parliament, government or judiciary of any rule of EU law intended to confer individual rights will entitle any individual sustaining damage as a direct result to compensation from the UK government…
  5. Thus, EU law in EU Treaties and EU legislation will pass into UK law through the medium of section 2(1) or the implementation provisions of section 2(2) of the 1972 Act, so long as the United Kingdom is party to the EU Treaties. Similarly, so long as the United Kingdom is party to the EU Treaties, UK courts are obliged (i) to interpret EU Treaties, Regulations and Directives in accordance with decisions of the Court of Justice, (ii) to refer unclear points of EU law to the Court of Justice, and (iii) to interpret all domestic legislation, if at all possible, so as to comply with EU law…. And, so long as the United Kingdom is party to the EU Treaties, UK citizens are able to recover damages from the UK government in cases where a decision of one of the organs of the state based on a serious error of EU law has caused them loss.
  6. In our view, then, although the 1972 Act gives effect to EU law, it is not itself the originating source of that law. It is, as was said on behalf of the Secretary of State echoing the illuminating analysis of Professor Finnis, the “conduit pipe” by which EU law is introduced into UK domestic law. So long as the 1972 Act remains in force, its effect is to constitute EU law an independent and overriding source of domestic law.

Does the 1972 Act preclude the use of prerogative power to withdraw?

  1. In short, the fact that EU law will no longer be part of UK domestic law if the United Kingdom withdraws from the EU Treaties does not mean that Parliament contemplated or intended that ministers could cause the United Kingdom to withdraw from the EU Treaties without prior Parliamentary approval. There is a vital difference between changes in domestic law resulting from variations in the content of EU law arising from new EU legislation, and changes in domestic law resulting from withdrawal by the United Kingdom from the European Union. The former involves changes in EU law, which are then brought into domestic law through section 2 of the 1972 Act. The latter involves a unilateral action by the relevant constitutional bodies which effects a fundamental change in the constitutional arrangements of the United Kingdom.
  2. One of the most fundamental functions of the constitution of any state is to identify the sources of its law. And, as explained in paras 61 to 66 above, the 1972 Act effectively constitutes EU law as an entirely new, independent and overriding source of domestic law, and the Court of Justice as a source of binding judicial decisions about its meaning. This proposition is indeed inherent in the Secretary of State’s metaphor of the 1972 Act as a conduit pipe by which EU law is brought into the domestic UK law. Upon the United Kingdom’s withdrawal from the European Union, EU law will cease to be a source of domestic law for the future (even if the Great Repeal Bill provides that some legal rules derived from it should remain in force or continue to apply to accrued rights and liabilities), decisions of the Court of Justice will (again depending on the precise terms of the Great Repeal Bill) be of no more than persuasive authority, and there will be no further references to that court from UK courts. Even those legal rules derived from EU law and transposed into UK law by domestic legislation will have a different status. They will no longer be paramount, but will be open to domestic repeal or amendment in ways that may be inconsistent with EU law.
  3. However, as explained above, the EU Treaties not only concern the international relations of the United Kingdom, they are a source of domestic law, and they are a source of domestic legal rights many of which are inextricably linked with domestic law from other sources. Accordingly, the Royal prerogative to make and unmake treaties, which operates wholly on the international plane, cannot be exercised in relation to the EU Treaties, at least in the absence of domestic sanction in appropriate statutory form. It follows that, rather than the Secretary of State being able to rely on the absence in the 1972 Act of any exclusion of the prerogative power to withdraw from the EU Treaties, the proper analysis is that, unless that Act positively created such a power in relation to those Treaties, it does not exist. And, once one rejects the contention that section 2 accommodates a ministerial power to withdraw from the EU Treaties… it is plain that the 1972 Act did not create such a power of withdrawal, as the Secretary of State properly accepts.
  4. We accept, of course, that it would have been open to Parliament to provide expressly that the constitutional arrangements and the EU rights introduced by the 1972 Act should themselves only prevail from time to time and for so long as the UK government did not decide otherwise, and in particular did not decide to withdraw from the EU Treaties. But we cannot accept that the 1972 Act did so provide. As Lord Hoffmann explained in R v Secretary of State for the Home Department, Ex p Simms [2000] 2 AC 115, 131,

“the principle of legality means that Parliament must squarely confront what it is doing and accept the political cost”, and so “[f]undamental rights cannot be overridden by general … words” in a statute, “because there is too great a risk that the full implications of their unqualified meaning may have passed unnoticed in the democratic process”.

Had the Bill which became the 1972 Act spelled out that ministers would be free to withdraw the United Kingdom from the EU Treaties, the implications of what Parliament was being asked to endorse would have been clear, and the courts would have so decided. But we must take the legislation as it is, and we cannot accept that, in Part I of the 1972 Act, Parliament “squarely confront[ed]” the notion that it was clothing ministers with the far-reaching and anomalous right to use a treaty-making power to remove an important source of domestic law and important domestic rights.

  1. In our judgment, far from indicating that ministers had the power to withdraw from the EU Treaties, the provisions of the 1972 Act, particularly when considered in the light of the unusual nature of those Treaties and the Act’s unusual legislative history, support the contrary view. As the Divisional Court said, the long title of the 1972 Act stated that its purpose was to make provision in connection with the “enlargement” of what is now the European Union, which is not easy to reconcile with a prerogative power to achieve the opposite. Similarly, the side-note to section 2, “General implementation of Treaties”, points away from a prerogative to terminate any implementation. In addition, there is the fact that the 1972 Act required ministers not to commit the United Kingdom to any new arrangement, whether it increased or decreased the potential volume and extent of EU law, without first being approved by Parliament – by statute in the case of a new EU Treaty and by an approved Order in Council in the case of a treaty ancillary to any existing EU Treaty. It would scarcely be compatible with those provisions if, in reliance on prerogative powers, ministers could unilaterally withdraw from the EU Treaties, thereby reducing the volume and extent of EU law which takes effect domestically to nil without the need for Parliamentary approval.

Conclusion on the effect of the 1972 Act

  1. Accordingly, we consider that, in light of the terms and effect of the 1972 Act, and subject to considering the effect of subsequent legislation and events, the prerogative could not be invoked by ministers to justify giving Notice: ministers require the authority of primary legislation before they can take that course.

Legislation and events after 1972: the 2015 Act and the referendum

  1. We turn to the 2015 Act and the ensuing referendum. The Attorney General …[i]n effect…said that, even though it was Parliament which required the referendum, the response to the referendum result should be a matter for ministers, and that it should not be constrained by the legal limitations which would have applied in the absence of the referendum.
  2. The referendum is a relatively new feature of UK constitutional practice. There have been three national referendums: on EEC membership in 1975, on the Parliamentary election voting system in 2011 and on EU membership in 2016…
  3. The effect of any particular referendum must depend on the terms of the statute which authorises it. Further, legislation authorising a referendum more often than not has provided for the consequences on the result. Thus, the authorising statute may enact a change in the law subject to the proviso that it is not to come into effect unless approved by a majority in the referendum….
  4. [Previous] statutes stipulated what should happen in response to the referendum result, and what changes in the law were to follow, and how they were to be effected…. By contrast, neither the 1975 Act nor the 2015 Act, which authorised referendums about membership of the European Community or European Union, made provision for any consequences of either possible outcome. They provided only that the referendum should be held, and they did so in substantially identical terms…
  5. It was suggested on behalf of the Secretary of State that, having referred the question whether to leave or remain to the electorate, Parliament cannot have intended that, upon the electorate voting to leave, the same question would be referred straight back to it. There are two problems with this argument. The first is that it assumes what it seeks to prove, namely that the referendum was intended by Parliament to have a legal effect as well as a political effect. The second problem is that the notion that Parliament would not envisage both a referendum and legislation being required to approve the same step is falsified by sections 2, 3 and 6 of the 2011 Act, which, as the Explanatory Notes (quoted in para 111 above) acknowledge, required just that – albeit in the more elegant way of stipulating for legislation whose effectiveness was conditional upon a concurring vote in a referendum.
  6. Where, as in this case, implementation of a referendum result requires a change in the law of the land, and statute has not provided for that change, the change in the law must be made in the only way in which the UK constitution permits, namely through Parliamentary legislation.


  1. What form such legislation should take is entirely a matter for Parliament. But, in the light of a point made in oral argument, it is right to add that the fact that Parliament may decide to content itself with a very brief statute is nothing to the point. There is no equivalence between the constitutional importance of a statute, or any other document, and its length or complexity. A notice under article 50(2) could no doubt be very short indeed, but that would not undermine its momentous significance. The essential point is that, if, as we consider, what would otherwise be a prerogative act would result in a change in domestic law, the act can only lawfully be carried out with the sanction of primary legislation enacted by the Queen in Parliament.
  2. Thus, the referendum of 2016 did not change the law in a way which would allow ministers to withdraw the United Kingdom from the European Union without legislation. But that in no way means that it is devoid of effect. It means that, unless and until acted on by Parliament, its force is political rather than legal. It has already shown itself to be of great political significance.
  3. It is instructive to see how the issue was addressed in ministers’ response to the 12th Report of Session 2009-10 of the House of Lords Select Committee on the Constitution (Referendums in the United Kingdom). The Committee included the following recommendation in para 197:

“[B]ecause of the sovereignty of Parliament, referendums cannot be legally binding in the UK, and are therefore advisory. However, it would be difficult for Parliament to ignore a decisive expression of public opinion.”

The UK government’s response as recorded in the Committee’s Fourth Report of Session 2010-11 was

“The Government agrees with this recommendation. Under the UK’s constitutional arrangements Parliament must be responsible for deciding whether or not to take action in response to a referendum result.”

[Abridged to highlight the important issues.]