A central plank in the reasoning of the Divisional Court in R (Miller) v Secretary of State for Exiting the European Union  EWHC 2768 at  is that ‘Absent such authority from the ECA [European Communities Act] 1972 or other statutes, the Crown cannot through the exercise of its prerogative powers alter the domestic law of the United Kingdom and modify rights acquired in domestic law under the ECA 1972 or the other legal effects of that Act.’
David Feldman argues that ‘the claim that the prerogative cannot be used to deprive people of rights, either absolutely or conditionally, is untenable as a matter of law.’ He goes further, questioning the proposition that ‘the foreign affairs prerogative operates only on the international plane, and cannot change domestic law’. He argues that ‘[t]he question in each case is whether the scope of the prerogative has been limited by Act of Parliament expressly or by necessary implication.’
I have analysed the authorities on which Professor Feldman relies in more detail elsewhere (Campbell McLachlan, Foreign Relations Law (CUP 2014, paper edn 2016)). The purpose of this brief intervention in the much larger debate about Miller is to demonstrate that the Court is indeed correct on this point. The cases, so far from calling the Court’s approach into question, in fact support it. I write therefore out of my great respect for Professor Feldman to engage with his argument and to indicate where and why I respectfully disagree with him.
It is essential that we are absolutely clear about this. Whatever the current perceived exigencies of Brexit, this point underpins the two most important elements of the Constitution of the United Kingdom (and cognate countries): the subjection of executive government to the rule of law and the supremacy of Parliament. These principles are so deeply entrenched that occasions on which the executive has seriously challenged them are few and far between. On such rare occasions (Walker v Baird  AC 491; Fitzgerald v Muldoon  2 NZLR 615), the courts have moved decisively to despatch the assertion of executive fiat. As Lord Hoffmann put it (Higgs v Minister of National Security  2 AC 228, 241): ‘The rule that treaties cannot alter the law of the land is but one facet of the more general principle that the Crown cannot change the law by the exercise of its powers under the prerogative. This was the great principle which was settled by the Civil War and the Glorious Revolution in the 17th century.’
In considering the cases, it is important to keep in mind the particular exercise of prerogative executive power in question in the present case–the power to enter into (and therefore also to withdraw from) treaties–and the ability of the executive to deploy that power to change the law of the United Kingdom. That is important because the prerogative powers relating to the principal functions of government are ‘finite, have been judicially recognised and described and cannot be extended further by those that exercise those powers or by decisions of the courts’ (C Vincenzi, Crown Powers, Subjects and Citizens (1998) 33).
What, then, are said to be the authorities to the contrary? I deal in turn with the principal cases relied upon by Professor Feldman.
The effect of the foreign affairs treaty prerogative on UK law was not at issue in R (Bancoult) v Secretary of State for Foreign & Commonwealth Affairs  UKHL 61,  AC 453. On the contrary, that case concerns the Crown’s prerogative power to legislate for a ceded colony. The ratio of the majority’s judgment rests on a distinction between the position within the United Kingdom and colonial rule. Lord Hoffmann holds at  that the Crown has no authority to expel anyone from England without statutory authority: ‘The Crown cannot remove this right by an exercise of the prerogative. That is because since the 17th century the prerogative has not empowered the Crown to change English common law or statute law. In a ceded colony, however, the Crown has plenary legislative authority. It can make or unmake the law of the land.’
By contrast, Attorney-General v De Keyser’s Royal Hotel Ltd  AC 508 does concern an act of the Crown at home: the requisition of a London hotel in wartime. But no question of the foreign affairs treaty prerogative arose in that case. The report of the decision does not support Professor Feldman’s conclusion that ‘it is clear from the speeches in De Keyser that, in the absence of statute occupying the field, the prerogative operates.’ Indeed, Lord Moulton holds at 549 that ‘This litigation itself is enough to show how debatable a proposition it would have been if the claim had been made that the ancient prerogative of the Crown covered the taking of a hotel in London for the more comfortable housing of a military staff and its clerks and typewriters. All such questions were put at rest by the Legislature giving express statutory authority by the Regulations.’
Burmah Oil Co (Burma Trading Ltd) v Lord Advocate  AC 75 concerned the exercise of the defence prerogative outside the UK. It did not involve the treaty-making power and was not concerned with the law applicable in the UK. The decision establishes the important principle that, where the Crown’s exercise of its war power abroad led to the destruction of property, compensation was payable. The House applied the principle of legality to executive action abroad affecting the rights of private individuals. The availability of the prerogative abroad (where UK law would not otherwise have applied) does not support the conclusion that this prerogative would have been available at home.
On the contrary, such a conclusion would be directly contrary to long-established principle confirmed in Walker v Baird  AC 491, 497. In that case, the Crown had sought to defend the seizure of a British subject’s property on British territory on the ground that its actions were justified by the exercise of its foreign affairs treaty-making power. Lord Herschell described the submission that the Crown’s acts could be justified as acts of state as ‘wholly untenable’. The Attorney General ‘conceded that he could not maintain the proposition that the Crown could sanction an invasion by its officers of the rights of private individuals whenever it was necessary in order to compel obedience to the provisions of a treaty’. The House found that the Crown’s more limited proposition that it might do so in order to avert a war did not arise.
The House returned to this question in Johnstone v Pedlar  AC 262, in which the Crown had seized the property of an American citizen involved in the Easter Rebellion in Ireland (then still British territory). The House held (at 273) that the principle in Walker v Baird was equally applicable within British territory to the national of a foreign friendly state who, being lawfully resident, is entitled to ‘the protection of British law’.
In this way, the specific rule that the use by the executive of its foreign affairs prerogative power to make (or unmake) treaties may not alter the law of the land supports the more fundamental principle of the Constitution, enshrined in s 1 Bill of Rights Act 1688, that precludes ‘the pretended power of dispensing with laws, or the execution of laws, by regal authority’.
The rule against use of the prerogative to change the law is not limited to Acts of Parliament, but applies to the law of the land more generally, as Lord Hoffmann held in Bancoult. Were it not so, the rule of law would be undermined, since the legal system consists not simply of statute, but all of the law of the land applied by the judges.
The Zamora  2 AC 77, decided in the midst of World War I, stands as important vindication of that fundamental principle. The Privy Council (at 90) dismissed as irrelevant the argument that the Prize Court owed its establishment to a prerogative act. It held: ‘The idea that the King in Council, or indeed any branch of the Executive, has power to prescribe or alter the law to be administered by Courts of law in this country is out of harmony with the principles of our Constitution.’ The Prize Court, though a municipal court, applies international law to its decisions. Acts of Parliament might bind the Court, but the Privy Council held (at 93) that this ‘affords no ground for arguing that they are bound by the executive orders of the King in Council.’
The Executive of the day was in no doubt about the import of the ruling and its significance. The Attorney General advised that ‘the Executive, cannot alter the law of the Court. Orders in Council which purport to do so are ultra vires and pro tanto a nullity’ (‘Report of the “Zamora” Committee’ FO 800/918, cited in Isabel Hull, A Scrap of Paper: Breaking and Making International Law during the Great War (2014) 180).
Council of Civil Service Unions (‘CCSU’) v Minister for the Civil Service  AC 374 was not a case about the exercise of the foreign affairs treaty-making prerogative or its effect on the general law of the land. It concerned an application for judicial review of an exercise of the Crown’s long-exercised power to regulate the terms of employment of its own Home Civil Service. A majority of their Lordships regarded the fact the source of the Crown’s power in the prerogative to be legally irrelevant (Lord Scarman at 407; Lord Diplock at 409; Lord Roskill at 417). The House decided that the power was, irrespective of its source, subject to the ordinary law of the land, in this case the principles of judicial review. But the fact that it had been exercised on grounds of national security meant that the Court would not disturb the executive’s decision.
The foreign affairs treaty power itself is not excluded by statute (though Parliament has chosen to impose important conditions on its exercise under Pt 2 Constitutional Reform and Governance Act 2010). But the executive has no power, whether by invoking the prerogative or otherwise, to change the law of the United Kingdom. Only Parliament may do that.
Those provisions of European Union law ‘as in accordance with the Treaties are without further enactment to be given legal effect or used in the United Kingdom’ are, by virtue of Parliament’s enactment of s 2(1) ECA, part of United Kingdom law. They ‘shall be recognised and available in law, and be enforced, followed and allowed accordingly’. They are, as Kerr LJ put it ‘part of the corpus juris of the member states’: Jensen v Corpn of the Trinity House of Deptford  2 Lloyd’s Rep 14, 26. They are as much a part of UK law as Magna Carta, Donoghue v Stevenson or the Road Traffic Acts.
‘It is’, as Lord Diplock said, ‘350 years and a Civil War too late for the Queen’s courts to broaden the prerogative. The limits within which the executive government may impose obligations or restraints upon citizens of the United Kingdom without any statutory authority are now well settled and incapable of extension.’ British Broadcasting Corp v Johns (HM Inspector of Taxes)  Ch 32.
Rights that are part of UK law may not be curtailed or removed by the exercise of the prerogative power to make or unmake treaties on the international plane.
I am grateful to Eirik Bjorge, Dawn Oliver and Rayner Thwaites for their comments on an earlier draft of this note.
Campbell McLachlan QC is Professor of Law at Victoria University of Wellington.
(Suggested citation: C. McLachlan, ‘The Foreign Affairs Treaty Prerogative and the Law of the Land’, U.K. Const. L. Blog (14th Nov 2016) (available at https://ukconstitutionallaw.org/))