Several joined cases are to be heard in the High Court in London early next month arguing that the UK Government is not legally entitled to notify the UK’s intention to withdraw from the European Union under Article 50 TEU without the prior approval of the UK Parliament. Other cases, raising somewhat different arguments, are also due to be heard in Belfast. Last week one set of the London claimants (the “People’s Challenge Interested Parties” (PCIP)) published their skeleton argument, and the Government has now also been required to publish its grounds of resistance.
Somewhat surprisingly, the PCIP case includes (amongst numerous others) an argument based on Article XVIII of the Union with Scotland Act 1706. This provides that the UK Parliament may make “no alteration … in Laws which concern private right Except for evident Utility of the Subjects within Scotland.” Reference to Article XVIII is surprising not least because it is being relied upon in an English court. Although Article XIX of the Acts of Union, which preserves the Court of Session and High Court of Justiciary, and prevents interference in matters of Scots Law by English courts, has been relied upon on a number of occasions, Article XVIII (to my knowledge) has not previously been invoked in an English case.
What is perhaps more surprising, though, is the reliance on Article XVIII to regulate the UK’s withdrawal from the EU given that it was also invoked – unsuccessfully – to challenge the UK’s accession to what was then the European Economic Community. In Gibson v Lord Advocate 1975 SLT 134, the owner of a Scottish fishing vessel sought to argue that the European Communities Act 1972 was invalid because the opening up of Scottish waters to vessels from other Member States would cause economic hardship to Scottish fishermen, thereby interfering with their traditional fishing rights in a manner which was not for the evident utility of the Scottish people. Lord Keith in the Outer House of the Court of Session rejected the claim primarily on the basis that fishing rights were matters of public right (which could be freely altered by the UK Parliament) rather than private rights. However, he also said that:
the question whether a particular Act of the United Kingdom Parliament altering a particular aspect of Scots private law is or is not “for the evident utility” of the subjects within Scotland is not a justiciable issue in this Court. The making of decisions upon what must essentially be a political matter is no part of the function of the Court, and it is highly undesirable that it should be.
The argument being made by the PCIP claimants in relation to Article XVIII is rather different. It forms part of a more general argument that the Government may not rely on Royal Prerogative powers relating to the conduct of foreign affairs to trigger Article 50 because to do so would lead to the removal of rights founded in EU law which can only be altered by Parliament. As regards Article XVIII, they argue, first, that the Acts of Union prevent modification of private law in Scotland except by the UK Parliament. Secondly, some rights derived from EU law, such as employment rights and consumer rights, are said to form part of Scots private law. And third, given the referendum result in Scotland, and subsequent statements by the Scottish Government, MSPs and Scottish MPs, they contend that it cannot be assumed that withdrawal of Scotland from the EU would be for the evident utility of the Scottish people. The point, however, is not whether the question of evident utility has been wrongly determined – the claimants accept that issue is non-justiciable; rather, they insist that Parliament must be given the opportunity to consider the question of evident utility and that it would be unlawful for the Government to pre-empt that consideration.
Leaving aside the broader question of whether triggering Article 50 does in fact interfere with EU law rights, it seems to me that every stage of the Article XVIII argument is fundamentally misconceived.
In the first place, it is questionable whether EU-derived rights should be included within the meaning of private rights for the purposes of Article XVIII. The aim of that provision was to regulate the extent to which the newly-formed Parliament of Great Britain could alter Scots law as it stood at the time of the Union. While laws concerning trade, customs and excises were to be made uniform, and the new Parliament was permitted to make laws concerning “publick right Policy and Civil Government” the same throughout the whole UK, the power to alter private law was made subject to the evident utility proviso. The aim was not to prevent change altogether, but rather to preserve the distinctive character of Scots private law by preventing its wholesale or unthinking assimilation to English law. However, since EU-derived rights are by definition not part of the traditional corpus of Scots private law, and are already the same in Scotland as in England, it would be a perversion of the purpose of Article XVIII to use it to prevent such rights being changed for Scotland alone.
Secondly, the argument that only the UK Parliament may alter Scots private law is clearly untenable. For a start, it was assumed at the time of the Union that Scots private law would continue to be developed by the Scottish courts – as has obviously been the case in practice. In addition, the Scottish Parliament has competence to alter Scots private law (subject to express reservations), and again has done so extensively. Even if one takes the view that the Scottish Parliament is a delegate of the UK Parliament (a characterisation that was rejected in AXA General Insurance Ltd v Lord Advocate  UKSC 46), it would be a stretch to say that the UK Parliament has considered the “evident utility” of every subsequent legislative change to private law by the Scottish Parliament.
Finally, it seems contradictory to use evidence that Scottish voters and politicians do not consider withdrawal from the EU to be for their evident utility to support a claim that the UK Parliament, in which Scottish representatives are a small minority, must authorise any change in Scots private law. Rather than providing special constitutional protection for Scots private law, the evident utility test is reduced to a mere formality, since it is not suggested that Parliament must take any special cognisance of the referendum result in Scotland, or make any distinct provision for Scots private law, nor, as already noted, is it argued that Parliament’s decision as to “evident utility” would be legally challengeable.
In sum, Article XVIII of the Acts of Union is an implausible ground on which to argue that the Royal Prerogative has been abrogated as regards withdrawal from the EU. Cynically, this might be regarded as an opportunistic attempt to add weight to the claimants’ case by alluding to the very real constitutional problems caused by the territorial differences in the EU referendum result, yet in a manner which does nothing meaningful to resolve those problems.
At the same time, however, the temptation to throw the constitutional kitchen sink at the Article 50 challenge illustrates the profound effect that EU membership has had on the UK’s constitution more generally. Advocates of Brexit hope, by removing the obligation to give supremacy to EU law, to restore the sovereignty of the UK Parliament. Yet the constitutionalisation of the legal order necessitated by EU membership has not been confined to the question of the relative hierarchy of EU and domestic laws, but has prompted judges and jurists to explore and crystallise the normative structure of the legal order more broadly. This constitutional spillover effect is unlikely to be reversed by Brexit. Indeed, should the Article 50 challenges succeed on some of the other grounds which have been raised, Brexit will itself have contributed to that process.
Aileen McHarg is Professor of Public Law at the University of Strathclyde
 See generally See JD Ford ‘The Legal Provisions in the Acts of Union’ (2007) 66 Cambridge Law Journal 106.