One of the extraordinary outcomes of the Brexit referendum has been the insistence that the Government is entitled to exercise its powers in relation to the Brexit process without involving Parliament. In a constitution whose central principle is Parliamentary sovereignty, such claims must be viewed with deep suspicion. Human rights are already precarious if left in the hands of a sovereign Parliament, especially where, as in the UK, the legislature is heavily dominated by the executive. This is even more so if Parliament can be sidestepped. It is therefore of immense importance that the High Court in Miller stepped in to protect the power of Parliament against the executive. Bickel argued 50 years ago that, in holding the balance of power between the legislature and the executive, the Court is the least dangerous branch. Bickel’s ringing claim holds most true when the Court acts, not to exert its own power, but to protect the power of Parliament.
It is telling that the Government invoked the royal prerogative to justify its claim to sidestep Parliament in relation to Article 50. As Lord Reid put in 1965: ‘The prerogative is really a relic of a past age, not lost by disuse but only available for a case not covered by Statute.’ (Burmah Oil (1965 AC 75 at 101) Only with the tacit acquiescence of Parliament can the continued existence of prerogative powers be reconciled with Parliamentary democracy. The Government therefore argued that Parliament should be regarded as having intended the executive to exercise the power to leave the EU without Parliamentary participation.
The Court’s rejection of this argument was based on its articulation of the fundamental constitutional principles which should inform statutory interpretation. In a system of Parliamentary sovereignty, against the reality of executive domination, the principle that Parliament is free to legislate as it wishes is subject to a strong presumption that it is aware of such constitutional principles and respectful of them. The court reiterated several such principles: most importantly, that Parliament does not intend to legislate in a way which defeats fundamental human rights or precludes access to the courts; and that the Crown cannot use its prerogative powers to alter domestic law. These presumptions can be overridden by Parliament, but the stronger the constitutional principle, the more difficult it is to rebut. This means that it is ultimately the court that has the responsibility for ensuring that Parliamentary sovereignty is exercised constitutionally.
The application of these principles has two important implications for the role of Parliament in relation to the Brexit process. Firstly, the Court held that in enacting the European Communities Act 1972, Parliament clearly intended EU rights to have effect in domestic law. This effect should not be capable of being overridden by the executive exercising its prerogative powers.
Secondly, despite claims that Parliament can be sidestepped because ‘the people have spoken’, the Court affirmed that, in law if not in politics, the result of the referendum was advisory only. Applying the strong principles of constitutional interpretation set out above, it held that the Referendum Act 2015 must be interpreted in the light of the basic constitutional principles of parliamentary sovereignty and representative parliamentary democracy. This meant that a referendum on any topic can only be advisory for Parliament unless very clear statutory language is used to rebut this presumption. The Referendum Act 2015 contained no such language.
The human rights implications of leaving the EU are profound, particularly in relation to the right to equality, a fundamental right in EU law. The Court acknowledged that a key right which will inevitably be lost will be the ability to refer to the CJEU in case of breach of such rights. At the same time, the future of the Human Rights Act remains precarious. With neither a justiciable bill of rights, nor the binding nature of EU rights, Parliament remains the last custodian of human rights in the UK. The High Court in Miller asserted a crucial judicial role in insisting on strong constitutional presumptions that Parliament does not intend to undermine fundamental human rights, and that the executive cannot at its own whim act in a way which undermines those rights. It is to be hoped that the Supreme Court upholds this position.
This is surely a far more convincing account than that of many commentators (eg Mark Elliot: weak on the rights argument, where Sandra feldman is so strong. My modest contribution is at https://dbfamilylaw.wordpress.com/2016/11/07/our-rights-the-miller-brexit-case-explained/. The extent to which rights, many of them fundamental, can be overridden is surely crucial to this (with an important echo in the advisory referendum point).
The novel presumption at  of Miller that “a referendum on any topic can only be advisory for the lawmakers in Parliament unless very clear language to the contrary is used in the referendum legislation in question” now falls to be considered by the Supreme Court – if an appeal is lodged now that a leapfrog certificate has been issued.
I contend this presumption is arguably the wrong way round (subject to compatibility with the principle of legality); it should be presumed that a referendum should be a statutory decision if the statute complies with the principle of legality.
I so contend because any presumption should comply with two constitutional principles that have had very little discussion: the principle of legitimacy and the principle of comity.
See Professor Richard Ekins: The Legitimacy of the Brexit Referendum on the UKCLA blog , whose concluded view seems to rest on these two constitutional principles
I believe, after reading the Hansard debates, that the mischief the 2015 Act was directed at was precisely to avoid Parliament taking a decision on the referendum question.
The application of the novel presumption at  of the Divisional Court judgment, and thus the ratio of the court’s decision, rests squarely on evidence extraneous to the statute namely “a clear briefing paper to parliamentarians explaining that the referendum would have advisory effect only”.
Relying on such extra-statutory Parliamentary material is arguably contrary to the authority, binding on the Divisional Court, of Pepper v Hart  AC 593 that only clear and uncorrected statements by a Government, or other proposer of a Bill should be given “weight” by the court.
Pepper was not cited before the Divisional Court nor referred to in the judgment.
Pepper is clearly relevant. The defence relied in its skeleton argument (and less clearly in oral argument) on clear and uncorrected statements by both Government proposers that the purpose of the Bill was to provide for a decision (“final say” was subject to correction but “decision” was not) .
See foonote 1 at p. 7 of the skeleton argument :
‘This was clearly stated on many occasions, for example: “This is a simple, but vital, piece of legislation. It has one clear purpose: to deliver on our promise to give the British people the final say on our EU membership in an in/out referendum by the end of 2017.” (Second Reading, HC, Hansard, 9 June 2015, col. 1047, the Foreign Secretary); “As the Prime Minister has made very clear, if the British people vote to leave, then we will leave. Should that happen, the Government would need to enter into the processes provided for under our international obligations, including those under Article 50 of the Treaty on European Union.” (Report stage, HL Hansard, 23 November 2015, col. 475, Minister of State, Foreign and Commonwealth Office, Baroness Anelay of St Johns). On 22 February 2016, the-then Prime Minister told the House of Commons that “This is a vital decision for the future of our country, and I believe we should also be clear that it is a final decision…This is a
straight democratic decision—staying in or leaving—and no Government can ignore that. Having a second renegotiation followed by a second referendum is not on the ballot paper. For a Prime Minister to ignore the express will of the British people to leave the EU would be not just wrong, but undemocratic.” (HC, Hansard, 22 February 2016, col. 24).’
This reference to “international obligations” (which was not argued orally at the hearing) is likely to be absolutely crucial to argument in any Supreme Court appeal, because it is crucial to construction of domestic statutes.
If, as I contend, the 2015 Act provided for the UK’s statutory decision to leave the EU then the obligation of notification in Article 50(2) would have to be read into the 2015 Act; this would impose an implied domestic duty on the Executive to fulfil the UK’s obligations under EU law to notify any decision lawfully made by the UK to leave the EU.
Remarkably, the Divisional Court failed to make any findings on whether the UK has made a lawful decision to leave the EU.
While such findings would have been obiter, they will be crucial to any appeal since the defence is likely to continue with its (I believe correct) contention that it is the decision to leave that has legal consequences on domestic rights/legislation and not the decision to notify as the claimants successfully contended.
Like most commentators, Professor Fredman focuses on the “human rights implications of leaving the EU”,
She correctly states these implications are “profound.”
However, this perspective ignores the equally profound “human rights implications” of staying in the EU.
Accepting the four movement freedoms of the EU (goods, workers, services, and capital) has profound human-rights implications, implications both positive and negative (which most commentators simply ignore), eg, on housing and employment.
If, as I contend on a Pepper v Hart reading, the referendum was the UK’s statutory decision to leave the EU then the referendum should be viewed, inter alia, as a statutory human-rights proportionality-balancing exercise by the statutory decision-maker specified in the 2015 Act : the UK electorate.
Far from being unlawful, from such a human-rights perspective, such a decision by such a statutory decision-maker would have the highest possible constitutional legitimacy and the full authority of Parliament, which enacted the 2015 Act.
Parliament is presumed to legislate in full knowledge of the law including the common-law rule of statutory interpretation in Pepper v Hart.
No such presumption can be made about court judgments because Counsel are under a duty to cite relevant authority to the Court, particularly in judicial review which is not adversarial because Counsel and all the parties have an overriding public-law duty to assist the Court in reaching the correct conclusion on legality.