The Supreme Court ruling in relation to Brexit was a thing of paradox. Many people who might normally be assumed to favour popular sovereignty went into ecstasy over a ruling which was a Diceyan reassertion of the sovereignty of Parliament as the guiding principle of the British constitution. It was a stark demonstration of the extent to which Brexit has become the ultimate test of political faith. Remainers embraced the sovereignty of parliament simply because the referendum, which they lost, had been an exercise in popular sovereignty. But these were English issues. Viewed from Scotland, this ruling carried a different message, not about whether sovereignty lay with the people or with parliament, but about which parliament was sovereign.
Although the Scottish Government was not party to the Brexit case, there was an intervention in the devolution aspect of it by the Lord Advocate on behalf of the Scottish government. The Scots had hoped that the case would lead to a ruling supporting FM Nicola Sturgeon’s position that Brexit could not proceed without the consent of the devolved nations.
Most of the devolution issues arise from the contention that the terms on which powers have been statutorily devolved to the administrations of Scotland, Wales and Northern Ireland are such that, unless Parliament provides for such withdrawal by a statute, it would not be possible for formal notice of the United Kingdom’s withdrawal from the EU Treaties to be given without first consulting or obtaining the agreement of the devolved legislatures…( UKSC 5, para 6)
The point of law in this regard, at least in relation to Scotland, turned on the Sewel Convention.
The Sewel Convention has its origins in a speech in the Lords by Lord Sewel during a debate on the 1998 Scotland Act
the devolution of legislative competence to the Scottish parliament does not affect the ability of Westminster to legislate for Scotland even in relation to devolved matters. […] However, as happened in Northern Ireland earlier in the century, we would expect a convention to be established that Westminster would not normally legislate with regard to devolved matters in Scotland without the consent of the Scottish parliament. (Hansard (HL Debates), 21 July 1998, col 791)
This convention was later included in a Memorandum of Understanding and Supplementary Agreements between the UK Government and the devolved governments (Cm 5240, 2001)
13. The United Kingdom Parliament retains authority to legislate on any issue, whether devolved or not.
It is ultimately for Parliament to decide what use to make of that power.
However, the UK Government will proceed in accordance with the convention that the UK Parliament would not normally legislate with regard to devolved matters except with the agreement of the devolved legislature. Memorandum of Understanding and Supplementary Agreements (CM 5240, 2001, p. 8)
An ‘Explanatory Note’ on page 4 stated that it ‘is not intended that these agreements should be legally binding’.
With regards to this, the Supreme Court judgement noted that ‘Para 2 of the Memorandum of Understanding stated that it was a statement of political intent and that it did not create legal obligations’[ UKSC 5, para 139]. The Court is here citing the 2013 version (presumably the most recent). The 2001 version of the Memorandum did not include this second paragraph, but the ‘explanatory note’ cited above had the same intent and effect.
The Sewel Convention remained merely a convention, and, as such, not justiciable. The court’s judgement was clear on this ‘It is well established that the courts of law cannot enforce a political convention’ ( UKSC 5, para 141)
In 2016 the Scotland Act 1998 Section 28 was amended to include
(8) But it 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.
This would appear to give a statutory basis for the Convention, elevating it from a merely political convention to a piece of legislation, but it should be noted that Clause 7 of section 28 of the original 1998 Act, which immediately precedes the above, was left intact:
(7) This section does not affect the power of the Parliament of the United Kingdom to make laws for Scotland.
In any case, the Supreme Court judgement recognised that the insertion of clause 28.8 meant that the Sewel Convention had received ‘statutory recognition’ ( UKSC 5, para 147), but added that:
by such provisions, the UK Parliament is not seeking to convert the Sewel Convention into a rule which can be interpreted, let alone enforced, by the courts; rather, it is recognising the convention for what it is, namely a political convention […]. That follows from the nature of the content, and is acknowledged by the words (“it is recognised” and “will not normally”), of the relevant subsection. We would have expected UK Parliament to have used other words if it were seeking to convert a convention into a legal rule justiciable by the courts. [ UKSC 5, para 148]
In other words, the clause gave the convention ‘recognition’ but no legal effect. Even the Bill of Rights was quoted to prove that the convention could not be enforced by any court ( UKSC 5, para 145).
In light of the above, it is hardly surprising that the Court upheld that
The Lord Advocate and the Counsel General for Wales were correct to acknowledge that the Scottish Parliament and the Welsh Assembly did not have a legal veto on the United Kingdom’s withdrawal from the European Union. ( UKSC 5, para 150)
Three Judges dissented from the Courts judgement on the main issue of the need for a vote in Parliament to trigger Article 50, Lord Reed, Lord Carnwath and Lord Hughes, but not a single judge dissented in relation to the Sewel Convention (see  UKSC 5, paras 242, 243 & 282).
No surprises here. Every mention of the convention, whether in Parliament, law or memoranda of understanding, is prefaced by or ringed with, caveats implying or boldly asserting the right of Parliament – Westminster – to legislate on any matter in Scotland, devolved or not, should it so chose – Sewel Convention or no Sewel Convention.
The Sewel Convention is not a Scottish version of the Statute of Westminster. The Supreme Court’s ruling was a reassertion of a basic fact of the British constitution – the sovereignty of (the Westminster) Parliament. Scotland’s (denied) right to veto Brexit was considered in terms of ‘devolution legislation’, ‘devolution arguments’ or ‘devolution issues’ (eg  UKSC 5, paras 6, 9 & 10). ‘Devolution’ is here the key term. The Scottish Parliament is not a sovereign body. Such powers as it has are simply powers devolved upon it from Westminster, the sovereign parliament.
First Minister Nicola Sturgeon’s reaction to the Supreme Court’s decision was to assert that even if there was no legal requirement for Westminster to seek the approval of the devolved governments prior to triggering Article 50, there is still a “clear political obligation to do so”. She is absolutely correct, but it absolutely will not happen. The Westminster Government is fully aware that if they gave the Scots the power to veto Brexit, they would use it; but, following the Supreme Court ruling, there is no legal requirement for London to give Scotland any such power.
Speaking after the Supreme Court judgement, the First Minister stated that:
The claims about Scotland being an equal partner are being exposed as nothing more than empty rhetoric and the very foundations of the devolution settlement that are supposed to protect our interests – such as the statutory embedding of the Sewel Convention – are being shown to be worthless. This raises fundamental issues above and beyond that of EU membership.
Sturgeon then raised the possibility of a second independence referendum. But she has not, yet, committed to holding one. Her reticence does not spring from any lingering affection for the UK state. The problem she faces is, as a former leader of the SNP, Gordon Wilson, expressed it in an article in the same ‘paper in which Sturgeon’s comments were reported:
The opinion polls show no movement in support for independence. It is almost as if the Scots people, through exhaustion, are in a catatonic trance. And yet there are calls for a gamble on a second referendum without adequate preparation. The Yes vote is just as likely to decrease as to surge. It defies common sense.
But Nicola Sturgeon has never been short of common sense. The dilemma she faces is that despite Brexit, the latest polls show support for independence has barely increased on the 2014 referendum result. And this has been consistent since the Brexit referendum. Sturgeon cannot risk losing a second independence referendum, it would put Scottish independence back by a generation.
Yet Scotland’s position within the UK is intolerable. Under the British constitution, it is irrelevant that 57 of Scotland’s 59 MPs are opposed to Brexit, irrelevant that Scotland voted two to one against Brexit in the referendum on that question, and irrelevant that Brexit is opposed by the parliament and government of Scotland. Regardless of whether or not there is a majority in favour of outright independence, the status quo reduces democracy in Scotland to a mockery in which neither (Scottish) popular nor (Scottish) parliamentary sovereignty apply.
Nor would any future ‘federal’ UK change this. Membership of the EU, like nuclear weapons and wars in the Middle East, is a matter of foreign policy, and foreign policy is invariably a matter reserved for central government, even in federal systems.
The logic of this situation may force the First Minister to opt for the gamble of a second Indyref. In any event, it is clear that Scotland’s current constitutional position is a democratic outrage. This is what Brexit in general, and the supreme court case in particular, has brought into sharp focus.