The​ constitutional questions around the government’s attempt to trigger Article 50 without parliamentary approval have been much discussed, but the EU referendum may well have another, more serious effect on the constitution. The UK’s membership of European organisations radically changed its constitution. For more than forty years domestic courts have interpreted Acts of Parliament in the light of EU legislation, giving precedence to the latter when a conflict arises, while under Section 3 of the Human Rights Act 1998, they have interpreted Acts of Parliament so as to make them compatible with human rights. These changes shook the foundations of the doctrine of parliamentary sovereignty, which holds that Parliament can make or unmake any law and that the role of the courts is to give effect to its will. Courts took on the task of protecting individuals against the vices present in any representative democracy: bias against unpopular minorities, neglect of the vulnerable, xenophobia, political opportunism, vested interests, abuse of power by powerful private actors and so on. They also began a process of institutional dialogue and co-operation with European supranational institutions in an attempt to tackle collective problems – such as climate change, consumer protection or workers’ rights – that no country can solve by itself.

Intellectually, however, the UK has been slow to admit the significance of these constitutional changes. They have tended to be conceptualised as compatible with, and grounded on, the doctrine of parliamentary sovereignty. Courts were depicted as applying the decisions of the EU or the European Court of Human Rights only because Parliament directed them to do so: when disapplying British parliamentary legislation courts were simply obeying Parliament. This interpretation salvages the doctrine of parliamentary sovereignty but deprives it of explanatory power.

The reality is quite different. In engaging with European legislation and case law, domestic courts were not obeying anyone; they were constructing their own view of how to interpret diverse legal sources (domestic and supranational) in a coherent and principled manner, and how to apply them in a way that respects equality before the law. In so doing, the courts were applying modern constitutionalism: the idea that there are certain fundamental legal principles, accepted and recognised in all mature democracies, which limit and control the effect of any decision made by government, however representative of the people it may be. Central to modern constitutionalism is the rule of law, which requires courts to uphold these principles, and the individual rights they encompass. In a rights-based constitutional democracy, no one is sovereign and no majoritarian decision, whether by the people or by Parliament, is above the rule of law.

It is disappointing that the Supreme Court reverted to the archaic notion of parliamentary sovereignty in the Miller judgment. Anxious to justify its decision that the executive doesn’t have the constitutional power to affect individual rights grounded in EU law, the majority subsumed these rights under the doctrine of parliamentary sovereignty. ‘Consistently with the principle of parliamentary sovereignty,’ the judgment held,

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 (i.e. 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.

But the real constitutional issue is not who gets to cancel the individual rights flowing from EU membership (Parliament or the executive), but whether these rights can be extinguished overnight. The Supreme Court judgment assumes that Parliament can do away with all such rights, make or unmake any law. But no political decision, not even a referendum, can do away with rule of law principles, such as protecting legitimate expectations and respecting the right to family and private life. Consider the case of the EU citizens who have made their lives in the UK and Britons who have made their lives elsewhere in the EU. Deporting someone on the basis of their nationality, when they have lawfully made their life in a country on the explicit understanding that they were entitled to permanent residence, would strike at the heart of the rule of law. Taking such rights away with no justification other than the outcome of a plebiscite may have a place in fascist and authoritarian regimes, but not in a constitutional democracy. Nobody may lawfully expel an EU citizen who has made their life in Britain, not even Parliament.

The term ‘rule of recognition’, which the Supreme Court cites in its judgment, comes from the work of H.L.A. Hart, professor of jurisprudence at Oxford and founder of modern legal positivism. Hart argued that the ‘rule of recognition’ was used by legal officials, including judges, to identify what counts as law within a legal system and who has supreme legislative authority. This rule exists through its application, through its being recognised as legitimate. The development of European law shows that the question of who is recognised as having supreme legislative authority (Westminster or Brussels) is a red herring; the main issue courts face is how to interpret a plurality of legal sources, which aren’t always hierarchically structured, in a principled way that respects the rights of litigants. Judges are bound to disagree frequently and to offer divergent interpretations of substantive principles of justice – as demonstrated by the fact that the Supreme Court judges were themselves divided on such a fundamental constitutional question as who possesses the authority to trigger Article 50. EU membership hasn’t so much changed the rule of recognition that applies to the UK constitution as challenged the existence of such a rule: UK courts, when deciding cases, are increasingly guided by the substance of the principles they apply, rather than by which body is ultimately sovereign under the system’s criteria of validity. Conceptualising the reception of EU law in terms of the rule of recognition fundamentally distorts the character of judicial practice.

It would be unfortunate if the reasoning of the Supreme Court in Miller foreshadowed the way the courts will handle potential violations of individual rights after Brexit. Infected by the majoritarianism that has spread through our institutions and our public culture, neither the prime minister nor the House of Commons has so far been willing to guarantee the legal rights of EU citizens who live in the UK. It is the duty of the courts not to fall under this spell in the name of the misconceived doctrine of parliamentary sovereignty, but to continue to enforce rights-based constitutionalism.

At the root of this majoritarian folly lies a misunderstanding about the nature of democracy. It is assumed that there is such a thing as ‘what the people want’, which is revealed in a majoritarian decision-making process and serves as the source of democratic legitimacy for specific laws. Yet this conception of democracy is deeply mistaken: voting – in general elections or referendums – is not a process aimed at revealing the desires and preferences of the people so they can be satisfied through legislation. If that were the case, there would be no need for reason-based deliberation and argument, which are central to any democratic process.

Arguments based on ‘what the people want’ are not only irrelevant in a democracy, but also ontologically spurious. Nothing can be revealed about what the people want in a process that serves a different function, that of constructing the vision of justice that should govern our polity. Winning a vote doesn’t mean no more argument is needed. Citizens are best viewed as participants, together with the three branches of government, in a complex process aimed at selecting, specifying and implementing particular conceptions of justice. As Ronald Dworkin observed, the ultimate basis of legitimacy is the substance of the principles of justice that underpin our laws, and over which no institutional actor, not even the electorate, has absolute control.

Referendums have a place in a representative democracy but their role is to complement it, not replace it. Their link to democratic legitimacy is tenuous and heavily conditioned. Far more than primary legislation, the outcome of a yes/no referendum leaves the content of the decision underdetermined, particularly when the question put to the people, as in the case of the EU referendum, affects an array of interconnected issues of law and policy. In most liberal democracies the use of referendums is strictly regulated by a written constitution that restricts the types of question that can be asked and the conditions under which they have a binding legal effect. The UK’s unwritten constitution lacks this rigid constitutional architecture. The experience of the EU referendum is another blow to the argument that the UK has no need for a written constitution.

Arguments based on the line that this is ‘what the people voted for’ are politically suspect. The political strategy of invoking the will of the people as a way of avoiding having to justify a decision, both before and after elections, captures the essence of the term populism. Populism should not be understood as an appeal to the emotions of the electorate and to rhetoric capable of mobilising large numbers of voters. Rather, it is the deliberate attempt to bypass the normal channels of representative democracy, and the institutional checks and balances it imposes, by invoking as the sole justification for political action the nebulous concept of what the majority of the people want, or what they voted for in the most recent election.

The idea that the EU referendum legitimised a particular conception of Brexit (so-called ‘hard’ Brexit) is impossible to justify. The only thing the referendum legitimised was the government’s mandate to seek a fair and just way of disentangling the country from decades of European integration, while honouring the fundamental principles of our legal tradition. Perhaps there is no way of doing this – in which case there should be no Brexit – or perhaps finding such a way requires securing a large proportion of the individual rights flowing from EU membership, including belonging to the single market. In either event, no betrayal of democracy would have taken place.

So the prime minister was right after all: Brexit does mean Brexit, which is another way of saying that – constitutionally speaking – it means nothing at all. The meaning of Brexit should be defined gradually through a long institutional process in which the three branches of government perform their constitutional roles, shaping our politics in the light of substantive principles of justice. But what is at stake is something more valuable than the UK’s relationship with Europe: it is the democratic nature of our politics, threatened by the majoritarianism that is spreading fast on both sides of the Atlantic.