This article first appeared in Scottish Legal News, 1 December 2016

Next week, the UK Supreme Court will hear arguments on whether the UK Government can rely on the royal prerogative to give notice to leave the EU, under Article 50 of the Treaty on European Union, or whether legislation is required. The Scottish Government will be intervening in the case, via the Lord Advocate James Wolffe QC, to argue that under Scots law the royal prerogative cannot be used. The Lord Advocate has published his written case, which includes the argument that the Scottish Parliament's consent should be sought before legislation is passed.

This argument concerns the constitutional convention that the UK Parliament will not normally legislate for Scotland on devolved matters, or alter the competence of the Scottish Parliament or responsibilities of the Scottish Government, without the Scottish Parliament's consent. The 'devolved matters' part of the convention was given statutory form earlier this year, when section 28(8) was added to the Scotland Act 1998: is recognised that the Parliament of the United Kingdom will not normally legislate with regard to devolved matters without the consent of the Scottish Parliament.

The legal and constitutional issues in this case, and in the Lord Advocate's written case in particular, are extremely complex and multi-layered. Some of the media coverage has misunderstood or glossed over the fundamental issues to which it gives rise. In particular, there appears to have been a focus in some quarters on the precise wording of section 28(8), and whether the word "normally means it does not apply in the specific circumstances of Brexit. However, there are fundamental questions that must be answered before the Supreme Court could even be in a position to decide that issue.

The key preliminary question is whether it is even competent for the courts to consider the application of section 28(8), or the underlying legislative consent convention: in other words, whether it is a "justiciable issue. The general rule is that constitutional conventions are not legally enforceable. In particular, there is a strong and long-standing constitutional principle that the courts cannot question the manner in which the UK Parliament conducts its business, even where a constitutional convention is concerned. So a failure to comply with a procedural or even a constitutional requirement during the passage of an Act of Parliament cannot invalidate that Act. Media coverage suggesting the Scottish Parliament could 'veto' Brexit, because the UK Parliament could not legislate without the Scottish Parliament's consent, is therefore incorrect.

The Lord Advocate recognises as much at paragraph 86 of his written case, stating that "if the UK Parliament were to choose to pass an Act of Parliament without the consent of the Scottish Parliament, the courts could not decline to recognise the validity of the resulting Act of Parliament. This is consistent with section 28(7) of the Scotland Act, which confirms that the UK Parliament retains the power to make laws for Scotland. The Lord Advocate is therefore not asking the Supreme Court to declare that any UK legislation authorising Article 50 can only be valid if the Scottish Parliament consents to it.

Instead, the Lord Advocate relies on the legislative consent convention as a reason to uphold the High Court's decision that giving the Article 50 notice requires authorising legislation. This line of argument encourages the Supreme Court simply to declare that such legislation would engage the legislative consent convention. If the Court is willing to do that, it would then be politically difficult for the UK Parliament to proceed without asking for consent, or despite a refusal of consent.

However, it remains to be seen whether the Supreme Court will be willing to even consider the issue in light of the general principle that conventions are not justiciable. The enactment of section 28(8) may not change that, given that it is hedged with the words "it is recognised that the UK Parliament will not "normally legislate on devolved matters without consent. Rather than arguing over whether Brexit is or is not a "normal circumstance, the UK Government is more likely to argue that that wording shows that Parliament was merely recognising the existence of the convention, and not giving the courts any authority to decide whether consent should be sought. It certainly took that position when section 28(8) was going through Parliament, as part of the Scotland Act 2016, despite several distinguished legally-qualified peers questioning whether that was correct.

Even if the Court proves willing to consider the question, there would still be an argument over whether legislative consent can be required where the UK Parliament is legislating in relation to a reserved matter (in this case foreign affairs, and specifically UK membership of the EU). The Lord Advocate concedes that legislation about leaving the EU would be outside the Scottish Parliament's competence, but argues that the consequential effects it would have on devolved matters would trigger the convention. The Supreme Court would have to address that issue in order to decide whether section 28(8) applies here.

It is simpler to argue that consent should be sought because leaving the EU would alter the competence of the Scottish Parliament and responsibilities of the Scottish Government, but the Scotland Act is silent on those aspects of the convention. The Lord Advocate argues that section 28(8) should be interpreted to include them. However, the Supreme Court may be more reluctant to make a declaration on those points than on the 'devolved matters' point, where there is at least some express statutory provision.

The legal complexity and political sensitivity of these issues may steer the Supreme Court towards deciding the case without offering a view on the legislative consent convention, as long as it is content that the right answer can be reached without having to take a decision on that issue. That would put the consent question back into the political arena, in which constitutional conventions are traditionally policed.

Some recent media coverage has also suggested that there could be a reference to the Court of Justice of the European Union in this case, but that seems extremely unlikely. Article 50(1) allows a Member State to decide to leave the EU "in accordance with its own constitutional requirements. Next week's case is about determining what the UK's constitutional requirements are in relation to the making of that decision. This is entirely a question for the UK courts, on which EU law does not and cannot have anything to say. The only EU law question that could potentially be relevant to this case, and on which a reference might be needed, would be whether the Article 50 notice can be withdrawn once given. However, the parties are agreed that the case can be decided on the basis that withdrawal is not possible, and the Lord Advocate has taken the same approach. A Supreme Court reference to the CJEU would therefore be very surprising. Far more likely is that the Supreme Court will decide the matter itself, with a decision expected early in the New Year if not before Christmas.

For more information, please contact Charles Livingstone (Partner in the public law and regulatory team at Brodies LLP).