I believe the Supreme Court will reject the appeal on behalf of the government of R (Miller) v Secretary of State for the Home Department. Having read the judgement the decision of the High Court comes down to two key things: (i) dualism and (ii) parliamentary sovereignty.
First, Britain has what is known as a “dualist” legal system. International law is only applicable domestically if transposed via domestic legislation. So for European Union (EU) law (directives and regulations) to be actionable, parliament passed the European Communities Act 1972 (EC 1972) . The crux of the issue surrounding the enactment of Article 50 and withdrawal from the EU is that the EC 1972 would have to be repealed and specific legislation (some form of EU Withdrawal Bill) drafted. Essentially, the EC 1972 acts to implicitly “abrogate” the Crown’s prerogative powers to be managed directly via statute. It creates a statutory duty, incorporating EU law, curtailing the power of the executive.
Process therefore is the cornerstone of the R (Miller) judgement. The judgement is not, as some more “vocal” sections of the press and everyone’s favourite professional Enoch Powell impersonator Mr Nigel Farage would have you believe, “blocking Brexit”. The judgement in R (Miller) asserted the primacy of the “bedrock” of the British constitution (see R (Jackson) v Attorney General  UKHL 56).
Secondly, we turn to parliamentary sovereignty. Britain’s constitution is “unwritten”(it is pieced together from the common law, jurisprudence and the actions of the legislature), there is no specific codified document (ala the US Constitution). The basis of the UK’s constitutional arrangement put simply is this:
“Parliament has the right to make or unmake any law whatever; and further, that no person or body is recognised by the law of England as having a right to override or set aside the legislation of Parliament” (See Post Office v Estuary Radio Ltd 1968)
The subordination of the “relic” of the “royal prerogative” power of the crown (i.e. the executive) finds its origins in The Case of Proclamations (1610). Here it stated:
“…the King hath no prerogative, but that which the law of the land allows him”. (See also The Zamora )
Thus, in order to to implement Article 50, the executive (as Theresa May said “Brexit means Brexit“) cannot unilaterally repeal domestic legislation. This must be done via the legislature (i.e. the sovereign body of our elected parliament). This is because the “royal prerogative” (while contended to hold authority with regard to international relations) cannot effect domestic legislation (i.e. the EC 1972 transposing EU law) unless:
“…parliament legislates to the contrary, the Crown should not have the power to vary the law of the land by the exercise of prerogative powers”.
So, to outline things simply: the EC 1972, to be repealed (in the activation of Article 50) must be via the sovereign legislature. In my opinion, even if Nigel Farage leads a march of 100,000 on the supreme court, the appeal of the government will be rejected. This is a matter of process on a point of law. It isn’t about stopping Brexit, but how Brexit is initiated. Many on the “leave” camp have for years and years moaned about the trampling of parliamentary sovereignty. Ironic they now do not understand what it means.
Frederick Gallucci – International Law LLM @GallucciFred