On November 23, 2022, the Supreme Court of the United Kingdom issued its unanimous decision in response to a reference by the Lord Advocate concerning whether the draft Scottish Independence Referendum Bill, which asks “should Scotland be an independent country?,” is outside the legislative competence of the Scottish Parliament because it refers to matters reserved to the Union or the UK Parliament under the Scotland Act of 1998. The Lord Advocate’s (senior law officer of the Scottish Government) reference was made under paragraph 34 of Schedule 6 to the Act. The Advocate General for Scotland (i.e., the Scottish law officer of the UK Government) asked “Does the provision of the proposed [Bill] . . . relate to reserved matters?” and whether, in particular it relates to the Union of the Kingdoms of Scotland and England and/or the UK Parliament.

After concluding that the answer to the Lord Advocate's question is yes, the proposed Bill relates to reserved matters and cannot be legislated, the Court addressed a number of arguments by the Scottish National Party (SNP – an intervener in the case) on self-determination and the principle of legality (¶¶ 84 et seq). The SNP argued that “the right to self-determination is a fundamental and inalienable right in international law and that there is a strong presumption in favour of the interpretation of domestic legislation in a manner which is compatible with international law.” In their view, a narrow reading of the phrase “relates to” would result in the Scottish Parliament being able to legislate for a “non-self-executing referendum in accordance with the right of the Scottish people to self-determination” whereas a broad interpretation of “relates to” would not. Accordingly, the SNP argued that “where two possible readings of a statutory provision are available, one of which is compatible with international law and the other which is not, the former should be preferred.” To support this contention, the SNP cited article 1 of the UN Charter, which enshrines the principle of self-determination of peoples. Moreover, the SNP relied on General Assembly Resolution 1514 of 1960, which refers to the right to self-determination, as does the ICCPR and the ICESCR.

In response to this, the Court acknowledged the “strong presumption in favour of interpreting [its] domestic law in a way which does not place the United Kingdom in breach of its obligations in international law,” but stresses that the presumption only applies “if the statutory provision is not clear on its face.” Moreover, the Court held that “the principle of self-determination is simply not in play here.” Citing prior case law in relation to the province of Quebec and Canada, as well as the UK’s submission to the ICJ in the case of Kosovo (2009), the Court pointed out that “‘international law favours the territorial integrity of States. Outside the context of self-determination, normally limited to situations of colonial type or those involving foreign occupation, it does not confer any “right to secede”.’” For the Court, “[those] observations apply with equal force to the position of Scotland and the people of Scotland within the United Kingdom.” In addition, the Court rejected the SNP’s use of self-determination as an interpretative tool supporting a narrow reading of “relates to,” holding that

[n]othing in the allocation of powers [in the Act], however widely or narrowly interpreted, infringes any principle of self-determination. On the contrary, the legislation establishes and promotes a system of devolution founded on principles of subsidiarity. It is now well established that devolution legislation such as the Scotland Act falls to be interpreted like any other statute, subject to the rules of interpretation set by the Act itself . . . . It would be inappropriate to apply any interpretative presumption with the purpose of achieving a greater or lesser devolution of powers.