Not for nothing has the Miller case, currently before the UK Supreme Court, been called one of the most important constitutional cases for decades.

In it, the UK Government is seeking to overturn the High Court in England and Wales’ decision last month that it does not have the power to trigger Article 50 TEU - i.e. to give notice of the UK’s intention to withdraw from the European Union - without the approval of the UK Parliament at Westminster. In addition, the Scottish Government, which has been granted permission to intervene in the case, is seeking to persuade the Supreme Court that not only is the approval of the UK Parliament required but so too is that of the Scottish Parliament.

The UK Parliament

The last few weeks have seen an outpouring of comment by constitutional lawyers on the case. One conclusion that may be drawn from that commentary is that the UK Government may well succeed in persuading the Supreme Court that the Crown’s prerogative in foreign affairs has not been abrogated or displaced by the European Communities Act 1972 - this being the principal basis on which the High Court came to its conclusion. It would indeed be difficult to explain much that has happened over the 40-odd years since the UK joined the EU had it been abrogated.

It by no means follows, however, that the Supreme Court will simply acquiesce in the proposition that the Government enjoys an unfettered discretion under the prerogative when it comes to triggering Article 50. The whole tenor of the development of judicial review over last half century is against the notion of an unfettered executive discretion, be it one based on statute or the prerogative.

The UK Government is likely therefore to have difficulty in persuading the Supreme Court that triggering Article 50 is a matter for it and it alone. And if one was looking for a doctrinal hook on which to hang such a conclusion, it would be the doctrine of legitimate expectations. The history of the UK’s relations with the European Union, including John Major’s decision to seek parliamentary approval before entering on the negotiations that led to the Maastricht treaty, provides ample support for the proposition that there is a legitimate expectation of parliamentary involvement before major decisions are taken or courses of action embarked upon. Indeed it is difficult to explain the extent of opposition to the Government’s claim that this is a matter for it alone other than on the basis of a legitimate expectation denied.

The Scottish Parliament

But if the UK Government is likely have difficulty in persuading the Supreme Court that it can proceed without parliamentary approval - that triggering Article 50 is a matter for it and it alone - the Scottish Government is likely to have much greater difficulty in persuading the Supreme Court that not only is the UK Parliament’s consent is required but so too is that of the Scottish Parliament. 

There is first the difficulty that the Scotland Act reserves international relations, including relations with the European Union; these are matters for the UK Parliament rather than the Scottish Parliament.

Secondly, there is the difficulty that, notwithstanding the fact that it has been recognised by statute, the Sewel convention is a political rule not a legal rule, i.e. a rule which is not justiciable in the courts.

As a political rule it is a matter ultimately for the Scottish Parliament's Presiding Officer and, in the absence of legislation at Westminster, it is not immediately obvious how the question arises. 

Quite apart from which there is the difficulty of the terms in which it is expressed – ‘[b]ut 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.’

Plus of course the consequentialist argument that to find in favour of the Scottish Government would be to hand the Scottish Parliament an effective veto, which the Scottish Government might not necessarily want, much as ‘remainers’ such as Peter Mandelson might wish the Scottish Parliament to have it.

Scottish consent

But if the Scottish Government fails in its attempt to persuade the Supreme Court that the UK Government cannot proceed without the Scottish Parliament’s consent, the question of Scottish consent will only have been delayed not settled.

I say ‘Scottish consent’ rather than the ‘Scottish Parliament’s consent’ because the UK Government’s widely trailed intention, should it lose the appeal, is to secure the enactment of a one clause bill authorising it to give notice under Article 50. 

But with a working majority of only 13, and an uncertain number of backbench remainers, the votes of the 54 SNP MPs could potentially be of crucial importance in securing the enactment of authorising legislation.

And then of course there is the question of the Scottish Parliament’s consent which will inevitably arise in the event of:

• adjustments being sought to the boundary between reserved and devolved matters, and /or
• the devolution settlement being amended to relieve the Scottish Parliament and the members of the Scottish Government of the obligation to act compatibly with EU law. 

Which raises some interesting questions, including whether there is a basis for a post-Brexit devolution settlement here whereby - in return for not blocking or derailing Brexit – Scotland gains … well what exactly? A section 30 order authorising a second independence referendum perhaps?