This article is by John-Paul Swoboda of 12 King’s Bench Walk

This case, concerning whether the Executive is entitled to use its prerogative powers to give notice under article 50 for the UK to cease to be a member of EU, is one of the most important legal decisions made during my lifetime. The case is of profound importance for two reasons. Firstly, the decision is of huge constitutional importance as it considers the relationship between parliament and the Executive. Secondly, the decision will, in my opinion, have a profound impact on Brexit.

The decision has been appealed by the Government to the Supreme Court, and the appeal is to be heard in December. The fact that the decision of the Divisional Court has been appealed does not detract from the importance of the decision and serves to highlight the importance of the issue to be resolved.

The Issue

The issue in the case is simple: is the executive entitled to give notice under article 50 for the UK to leave the EU using its prerogative powers?

Although the issue is simple its resolution is not because, on the facts, two rules of constitutional law appear to conflict. One rule of constitutional law is that the executive has no power to prescribe or alter domestic law; that is purely a matter for Parliament (‘the first rule’). This rule was considered in The Zamora [1916] 2 AC 77 at 90: “The idea that the… Executive, has the power to prescribe or alter the law… in this country is out of harmony with the principles of our Constitution.” The other rule of constitutional law relevant to this case is that the Executive exercising its prerogative powers may conduct international relations including the making and unmaking of Treaties on behalf of the UK (‘the second rule’).

The reason that the second rule does not, in normal circumstances, offend the UK’s most fundamental rule of constitutional law, that Parliament is sovereign and law enacted by Parliament is supreme, is because the second rule operates on the ‘international plane’ as opposed to the ‘domestic plane’. In other words, any treaties made or unmade by the Executive will not increase, diminish or dispense with the rights of individuals without the intervention of Parliament.

The particular feature of Brexit which gives rise to the conflict between the first and the second rule is that the European Communities Act 1972 (‘ECA’) (in particular section 2(1)) transcribes “rights … created or arising under the [EU Treaties]into the plane of domestic law. In other words, the rights provided for on the international plane, under the EU Treaties, are given “legal effect” on the domestic plane.

The particular rights which have arisen under EU law and been transcribed into domestic law were put into three categories by the Divisional Court: (i) rights which could, but need not, be replicated under domestic legislation (e.g. the rights in the Working Time Directive, or under the Package Travel Directive), (ii) rights which British Citizens enjoy in other member states as a result of the UK’s membership in the EU (e.g. the right to travel, live and work in other member states), and (iii) other rights which could not be replicated if the UK leaves the EU (e.g. the right to seek to persuade the EU commission to take regulatory action, or to seek a reference from the CJEU).

The problem that arises can be described as follows: if the Executive is permitted to use its prerogative powers to trigger article 50, which necessarily will lead to Brexit, it will diminish and remove rights of individuals which is contrary to the first rule (that the Executive has no power to prescribe of alter domestic law). However, if the Executive is not permitted to use its prerogative powers to trigger article 50 but must rather rely on authorisation from Parliament to trigger article 50, the second rule (the conduct of international relations including the making and unmaking of treaties) is undermined.

The Resolution of the Issue

The Divisional Court found that the first rule must prevail over the second rule in these particular circumstances. This Secretary of State’s argument was rejected because there was no basis to find that Parliament must have intended, by enactment of the ECA, to allow the Executive to unmake the existing EU Treaties even though this would have an effect on domestic law and rights. The Divisional Court found that there was nothing in the text of the ECA to suggest that the Executive had been given this power by Parliament and that if Parliament had intended to give the Executive this power it would have needed to be clear given the rule of statutory interpretation that legislation is to be interpreted in conformity with constitutional principles. To the contrary, the Divisional Court found that there were eight points, to be taken from the text of the ECA, which supported the proposition that Parliament did not intend to extend the Executive’s prerogative powers so that it could remove rights by unmaking the EU Treaties.

Dealing with the other side of the argument, the Divisional Court found that the ECA must be interpreted as abrogating the Executive’s power to unmake the EU Treaties. A number of cases were cited in support of this proposition including Laker Airways Ltd v Department of Trade [1977] QB 643 (CA). This case involved an international treaty which led to a statutory scheme for the licensing of air carriers. One of the air carriers licensed under the statutory scheme was Laker Airways Ltd. The Executive sought to nullify Laker Airways Ltd licence by unmaking and amending a part of the relevant Treaty. The Court of Appeal, with the lead judgment from Lord Denning MR, found that the statutory scheme had abrogated the Executive’s power to act in such a way. The parallel with the ECA is obvious; the Executive entered into EU Treaties, and once the Treaties were given domestic effect by the ECA it was no longer open to the Executive to nullify the ECA by unmaking the EU Treaties, by triggering article 50.


I have no crystal ball in which to look to see how the Supreme Court will eventually determine this issue but, in this author’s opinion, the decision of the Divisional Court was the correct one. There is a massive imbalance in importance between the constitutional rule that the Executive has no power to prescribe or alter domestic law and the other constitutional rule that the Executive exercising its prerogative powers may conduct international relations including the making and unmaking of Treaties on behalf of the UK.

The first rule has been of fundamental importance in the UK’s constitution for a long time. As Sir Edward Cooke stated in The Case of Proclamations (1610), “the King [Executive] by his proclamation or other ways cannot change any part of the common law, or statue law, or customs of the realm.” Similar provisions are to be found in section 1 of the Bill of Rights 1688. The first rule is a key facet of the most fundamental rule of the UK constitution: parliamentary sovereignty.

The second rule, by contrast, is a residual power which is necessarily secondary to the fundamental rule of parliamentary sovereignty. As was stated by Lord Reid in Burmah Oil Co (Burmah Trading) Ltd v Lord Advocate [1965] AC 75, 101: “The prerogative is really a relic of a past age, not lost by disuse, but only available for a case not covered by statue.”

In the absence of clear text in the ECA that Parliament intended to preserve the Executive’s prerogative power in relation to the EU Treaties at the expense of domestic rights transcribed from EU law into domestic law, it is my opinion that the first rule must prevail.

As commented upon in the introduction to this article, should the decision be upheld in the Supreme Court there are likely to be profound consequences as Parliament will need to pass legislation to enable article 50 to be triggered. It is inevitable, in my opinion, that for such legislation to be passed (if agreement can be reached by a majority of parliamentarians to trigger article 50) Parliament will have numerous demands.

John-Paul Swoboda

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