Since the 2016 Brexit referendum, the Scottish government has continued to repeatedly insist on the need for another independence referendum. Scotland's First Minister Nicola Sturgeon justifies this new consultation on the grounds that the United Kingdom's exit from the European Union has significantly altered the terms of the Union between Scotland and the rest of the United Kingdom, which, in the eyes of the Scottish National Party (SNP), invalidates the 2014 result.

However, so far, the British government has refused to agree to hold a new lawful referendum, as it did eight years ago. In the face of this refusal, Sturgeon has shown her determination to organize a referendum later this year. In this context, the Lord Advocate (the Scottish government's main legal adviser) submitted a reference to the UK Supreme Court on whether a bill drafted by the Scottish government on a consultative referendum on Scottish independence would fall within the powers of the Scottish Parliament. That is, whether Scotland can unilaterally organize an independence referendum in the same way that Canadian provinces can, and that the Autonomous Communities in Spain, the Länder in Germany and the regions in Italy, are forbidden to.

Before analyzing the Supreme Court's decision, it is worth making a few points about British constitutional law. It is well known that the United Kingdom does not have a constitution that entirely follows the form of a rigid written document in the style of the vast majority of constitutional states. It does however have its own constitutional law, partly written and partly reflected in general principles of law recognized by both Parliament and the courts.

Having made these clarifications, we turn to the above-mentioned Supreme Court decision, published on 23 November 2022, on Scotland's powers to unilaterally organize an independence referendum. The Court devotes the first few pages to examining questions of admissibility. There had been some controversy among British constitutionalists as to whether the legal basis for this consultation was section 33 or 34 of the Scotland Act,⁴ the latter provision being the one on which the Supreme Court relies. Section 34 can be understood as a residual clause allowing any other question relating to “devolved matters”" or the territorial Parliament to be referred to. Moreover, the Court decided not to use its discretionary powers to reject the consultation, as the British government had requested and as it had done on other occasions. Considering that this is a legal question of great practical importance, and it is in the public interest that the Court takes on the task of providing a legal answer. “The answer to the question will have practical consequences: it will determine whether the proposed Bill is introduced into the Scottish Parliament or not. The question is therefore not hypothetical, academic or premature.” (para 53).

The Court then goes on to consider the merits of the case briefly: what must be determined is whether a referendum on independence as proposed in the Scottish Government’s draft legislation “relates to” matters reserved to the United Kingdom Parliament of those mentioned in the Scotland Act 1998. For if that is the case, as already indicated, the organization of the referendum would be outside Scotland's powers. The Court has previously held that the purpose of paragraph 1 of Schedule 5 is that those matters in which the Union has an interest should remain the responsibility of the UK Parliament (for example, in Imperial Tobacco [2012] UKSC 61, para 29).

Finally, the Court also has examined an argument raised by the SNP concerning the right to self-determination. The Supreme Court rejects that this public international law right has any application in this case and refers to the well-known 1998 Supreme Court of Canada decision on the secession of Quebec. The Court considers that the arguments applied to Quebec back then are equally relevant to the case of Scotland: “In our view these observations apply with equal force to the position of Scotland and the people of Scotland within the United Kingdom.” (para. 89). Following Canadian reasoning, the British Supreme Court assumes that the right to external self-determination, which could lead to secession, applies in situations of former colonies or oppressed peoples only. This is not the case in Scotland, which has institutions of self-government (internal self-determination).

Consequently, if the Scottish government wants to lawfully organize a new independence referendum, it will have to reach an agreement with the British government, as was done in the past (Agreement of 15 October 2012). The British Parliament amended the Scotland Act to temporarily give Scotland, through an ad hoc Order in Council, the power to organize a referendum. But that power had been exhausted by the time of the 2014 referendum. In any case, even if no agreement is reached and, therefore, no lawful referendum is possible, it does not seem that the Scottish government intends to initiate an insurrectionary route. However, the SNP can present the next elections to the Westminster Parliament in Scotland as a “plebiscite” to ensure the mobilization of its electoral base.⁶

It is commonplace in comparative constitutional law to speak of the flexibility of British constitutionalism. It has even been argued, when analyzing the different ways in which the legal systems of liberal democracies deal with secession claims, that the British model, together with the Canadian model, represent a “new paradigm”⁷, far removed from the rigidities of the classic American and continental European models. However, and taking into account the differences between the United Kingdom and the states with rigid constitutions, at least on such an important point as determining who should decide on the secession of a territory, there are more similarities than differences between the old and the new paradigm, and this recent decision demonstrates this. The democratic principle, understood as the expression of the electoral body’s sovereign will over the territorial entity affected, cannot, on its own, alter the scheme of vertical distribution of powers or even be proposed through a unilateral consultative referendum, since what is in the common interest must be decided by the institution that represents the people as a whole. As can be seen, the migration of constitutional ideas in the field of responses to claims of secession continues and, on this occasion, not only crosses the Atlantic Ocean, but the English Channel too.