This note aims to address one of the many constitutional issues that have arisen in the aftermath of the United Kingdom’s referendum on its membership to the European Union. The electorate, by a relatively slim majority, have voted to leave the EU, and in response EU leaders have invited the UK to initiate the ‘Brexit’ process by invoking Article 50 of the Lisbon Treaty that provides the procedure to be followed by any member state wishing to withdraw from the European Union.
Article 50 provides that:
1. Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.
2. A Member State which decides to withdraw shall notify the European Council of its intention.
This seemingly straight-forward procedure has already caused a great deal of debate among constitutional lawyers, as the uncodified British constitution does not provide for a readily identifiable path to be followed under such circumstances. This uncertainty is further compounded by the fact that the European Union Referendum Act 2015 is, perhaps intentionally, silent on the procedure to be followed after a Leave victory.
The main issue that the note seeks to address, is whether Scotland can effectively veto Brexit as the Scottish government through comments of its First Minister has suggested. While the short answer would be that it probably could not, a closer inspection reveals a series of legal complexities that are worth addressing. The article will attempt to untangle this complicated constitutional web in the following manner. Firstly, it will address a key preliminary question that has been the source of disagreement for constitutional lawyers. This relates to the role of Parliament in the Brexit process. While it is clear that Parliament will be heavily involved in the laborious task of untangling EU law from domestic law, is Parliamentary consent also required before the PM can trigger the Article 50 process? For reasons that will be developed below, if the answer is in the negative, the scope of Scottish resistance to Brexit is severely diminished. If the answer is in the affirmative, then some stronger role for Scotland can be envisioned, but, in the author’s opinion, this would still in all probability not suffice to effectively ‘block’ Brexit. The article will examine both these eventualities in turn and attempt to define the role that Scotland could play in each of these potential outcomes.
Before examining this in greater detail, two introductory points relating to the British constitutional arrangements need to be discussed.
Firstly, Parliamentary sovereignty. This is a fundamental principle of the UK’s political constitution, that stipulates that the Westminster Parliament (WP) is sovereign, ie that there are prima facie no limits to its legislative authority. In its orthodox articulation, the principle specifies that courts cannot override the will of the WP by striking down primary legislation and consequently, the constraints on the WP’s legislative power are political rather than legal.
Secondly, some background information to the Scottish devolution arrangements would be useful. Unlike the WP, the Scottish Parliament (SP) is one of defined competence and therefore can only legislate in specific ‘devolved areas’ that are contained in the Scotland Act 1998 (SA 1998). Its competency is further restrained by clauses in the SA 1998 that require all legislation passed by the SP to be fully compliant with EU law and the European Convention on Human Rights. It is crucial to note, however, that the devolution arrangements are designed in such a way as to ensure that the WP retains its sovereignty with regard to Scotland, and is thus still in principle able to legislate on matters that fall under devolved competence. However, at the time the devolution arrangements were being drafted, a constitutional convention named the ‘Sewel Convention’ was established precisely to ensure that the WP would not arbitrarily legislate on devolved issues. This constitutional convention set two important constitutional restrictions on the WPs ability to legislate for Scotland. Firstly, the convention stipulates that the WP “would not normally legislate with regard to devolved matters in Scotland without the consent of the Scottish Parliament”. Secondly, and this is more important for the issue under discussion, the convention would be triggered and consent would be required whenever the WP attempted to legislate on matters which, although reserved, “affect the breadth of the devolved institutions' powers - i.e. the legislative competence of the Scottish Parliament or the executive competence of the Scottish Ministers”. As Brexit would most certainly affect the legislative competence of the SP for reasons that will be explained below, Scottish consent would in principle be required before the WP takes any legislative steps in the direction of Brexit. If no such consent is given, any action by the WP in this regard would be a breach of the convention. This, the Scottish government seems to argue, would be an insurmountable obstacle to Brexit. The note will proceed to argue why, in all likelihood, this would not be the case.
Is Parliamentary consent required for Article 50 to be triggered?
The preliminary issue to be addressed before examining Scotland’s role in Brexit, is whether there is a constitutional requirement for the Prime Minister to seek approval from the WP before she or he triggers Article 50 and begins the countdown to ‘Brexit’. Some constitutional scholars suggest that Parliamentary democracy requires that any action of such monumental constitutional significance must be preceded by Parliamentary authorisation, especially when the advisory nature of the referendum is taken into account. In the UK’s constitutional order, it should be Parliament and not government that has “the final say on the implications of the referendum”. Additionally, the fact that UK citizens will be deprived of rights associated with the EU, strengthens the argument that it would be a “legally ineffective” act for the government to single-handedly proceed with such a step. Others argue that the government’s prerogative power to conduct foreign policy - and therefore to enter or withdraw from treaties - allows the PM to proceed to the Article 50 (2) notification without first seeking Parliamentary consent.
From the perspective of Scotland, however, the path that is chosen has serious repercussions.
Could the Sewel Convention stop Brexit?
It is quite clear that one of the consequences of the UK leaving the EU, would be that the SP’s legislative competence would be altered since it will no longer be required to legislate in compliance with EU law. Thus, the Sewel Convention is, in principle, engaged.
With this in mind, the note will proceed to examine the contingencies from such an outcome.
1) Article 50 is triggered without Parliamentary consent.
In this scenario, the Sewel Convention would not immediately be engaged as the decision to initiate the Brexit process would not firstgo through the WP. However, it would be wrong to assume that Scottish consent on Brexit would altogether be bypassed. As part of the Brexit process, the WP would have to repeal the European Communities Act 1972 and also, renegotiate the devolution agreement in order to remove references to EU law from the SA 1998. This would engage the Sewel Convention. Whether this would be enough, however, to stop Brexit is doubtful. Unless Article 49 of the Treaty is invoked, or EU member states agree to the contrary, triggering Article 50 sets the UK on an irreversible, two-year path to Brexit. At the end of this process, the UK as a matter of international law will no longer be a member of the EU. From this international perspective, the internal constitutional problems of implementing Brexit at the domestic level are of no relevance. UK membership to the EU would cease and it would be up to the UK to resolve its internal constitutional crisis with Scotland and other devolved territories.
2) Article 50 can only be triggered after the WP votes to this effect.
In this scenario it is safe to assume that Scottish consent for Brexit would not be given. If the WP was to legislate contrary to Scotland’s consent, it would be doing so in breach of the Sewel Convention. Would this be an insurmountable obstacle to Brexit?
In order to respond to this question, it is important to first understand the role of constitutional conventions. Conventions in the UK’s constitutional arrangements are unwritten constitutional rules that are only politically binding. This entails that they cannot be legally enforced by courts and thus the validity of any WP primary legislation cannot be struck down by a legal challenge on the ground that the convention was not upheld. Thus, in strictly legal terms, withholding consent to Brexit is not a serious legal hurdle for the WP to legislate in spite of Scotland’s lack of consent. The sovereignty of the WP is not legally constrained by conventions, although the political repercussions of a breach of the Sewel Convention would be enormous and certainly provide further fuel to calls for Scottish independence.
Others argue that a breach of the convention, even though it does not carry legal consequences, would very much be an unconstitutional action and thus the prerequisite for triggering Article 50 in accordance with internal “constitutional requirements” could not be met. It would be difficult however to envision a way for this to be challenged. It is doubtful that any legal challenges, both at the domestic or European level, calling for the notification under Article 50 to be quashed on the ground that it was triggered unconstitutionally have any serious prospects of success, especially in light of the foundational principle of the British Constitution, Parliamentary sovereignty. It is safe to assume that if the WP were to legislate contrary to Scotland’s consent or if the UK government were to entirely, bypass Parliament and single-handedly trigger Article 50, little could be done to reverse this.
Dr Dimitrios Kagiaros, Teaching Fellow in Public Law and Human Rights, University of Edinburgh.
 Although it may not differ much in this respect from many states with codified constitutional rules.
 This aspect of the convention has been placed under statutory footing in the recent Scotland Act 2016.
 Reserved powers are the powers that are not devolved to the Scottish Parliament. It would be outside the competence of the Scottish Parliament to legislate in a reserved area.
 N. Barber, T. Hickman and J. King, ‘Pulling the Article 50 ‘Trigger’: Parliament’s Indispensable Role’, U.K. Const. L. Blog (27th Jun 2016) (available at https://ukconstitutionallaw.org/2016/06/27/nick-barber-tom-hickman-and-jeff-king-pulling-the-article-50-trigger-parliaments-indispensable-role/ .
 If, however, Parliament needs to be consulted, then another interesting issue arises. Could Parliament ignore the referendum outcome and vote in favour to remain in the UK? Legally speaking, and based on the definition of Parliamentary sovereignty provided above, the outcome of an advisory referendum like the one in question does not bind the sovereign WP to give its consent to Brexit. Politically speaking, however, it would be unlikely for Parliament – even though the majority of MPs and political Parties in Parliament were on the Remain camp- to go against the referendum result. The lack of a legal commitment to the referendum result, does not also mean that there is not a strong political commitment in this direction. For more on this see S. Douglas-Scott, ‘Brexit, the Referendum and the UK Parliament: Some Questions about Sovereignty’, U.K. Constitutional Law Blog (28th June 2016) available at https://ukconstitutionallaw.org/2016/06/28/sionaidh-douglas-scott-brexit-the-referendum-and-the-uk-parliament-some-questions-about-sovereignty/ .
 N. Barber, T. Hickman and J. King, ‘Pulling the Article 50 ‘Trigger’: Parliament’s Indispensable Role’, U.K. Const. L. Blog (27th Jun 2016) available at https://ukconstitutionallaw.org/2016/06/27/nick-barber-tom-hickman-and-jeff-king-pulling-the-article-50-trigger-parliaments-indispensable-role/
 See Mark Elliott, ‘Can Scotland block Brexit’? Public Law for Everyone (26th June 2016) available at https://publiclawforeveryone.com/2016/06/26/brexit-can-scotland-block-brexit/ and Carl Gardner, ‘Article 50 and UK Constitutional Law’ (27th June 2016) available at http://www.headoflegal.com/2016/06/27/article-50-and-uk-constitutional-law/
 Or according to an orthodox view on Parliamentary sovereignty, on any grounds whatsoever.
 J. Murkens, ‘Brexit: The Devolution Dimension’, U.K. Constitutional Law Blog (28th Jun 2016) available at https://ukconstitutionallaw.org/2016/06/28/jo-murkens-brexit-the-devolution-dimension/ and David Allen Green, ‘Article 50: Where are we now?’ Jack of Kent blog (26th June 2016) available at http://jackofkent.com/2016/06/where-we-are-now-with-article-50-decision-notify-and-devolution-issues/ .