The Impact of Public International Law on UK Courts

By Grace Etheredge

Although international law is often referred to by politicians and pundits in equal measure, it is an area of law that seems very difficult to pin down. This is partly due to its ability to manifest in many different forms and to thus have varying degrees of tangible effects in day to day affairs. While international law is thus too broad a church to fully expand upon in this article, I will give a brief outline of the way in which public international law impacts the UK legal system.


Historically, international law has been primarily concerned with the activities of states (Article 2.1 of the Vienna Convention on the Law of Treaties) and is thus often associated with treaties. This type is known as public international law and exists in forms such as the 1971 Five Power Defence Arrangement and the 2011 Arctic Search and Rescue Agreement. It stands in contrast to private international law which is focused on the regulation and resolution of disputes between private bodies such as corporations.

Among other things, it has thus been observed that public international law was initially conceptualized as operating beyond the concerns of individuals and outside the realms of domestic legal systems. In fact, the school of international realism asserted that the only crucial factor which affected a state’s decision to uphold its treaty obligations, was the threat of reputational repercussions if it did not.

Crucially, however, a state’s compliance is linked to its domestic courts. In common law jurisdictions, this is because judges interpret and develop the law with reference to their government’s international commitments. The extent to which international law can be drawn upon though, depends upon the level of incorporation permitted by Parliament.


The UK falls into the category of a dualist state which means that it practices a two-tier process of international treaty adoption and incorporation. The first part of it rests with the executive branch of government which uses the common law residue of its royal prerogative power to adopt and, when required, ratify treaties (subject to the 2010 Constitutional Reform and Governance Act). While this demonstrates the UK’s willingness to be bound (Article 14 of the Vienna Convention), the treaty in question is effectively non-justiciable until it has been incorporated into domestic law (JH Rayner Ltd v Department of Trade and Industry). This means that it cannot be given direct effect to bestow rights or obligations upon national persons. As explained by Lord Kerr, this dualist system is vital to prevent the executive from unconstitutionally enhancing its powers through international treaties or imposing obligations upon individuals without the oversight of Parliament.

The second level to the UK’s dualist system is the incorporation of a treaty into domestic law and this acts as a safeguard on the abuse of power. It is unusual, however, for a treaty to be directly incorporated into domestic law (see the modification of the European Convention on Human Rights in the Human Rights Act). This means that even when international treaties make it into domestic law, they are often adapted to suit domestic priorities and so have a different application in UK courts to other countries. They are thus not so much incorporated as given direct effect. This nonetheless means, however, that judicial interpretation and the process of judicial review can be used to hold the government of the day to the legal principles and objectives it committed itself to at the international level.

There are three main levels to public international law in the UK and they each perform a different function -

  1. Ratified but unincorporated international treaty law;

  2. International treaty law that has been given direct effect;

  3. The directly incorporated legal regime of the European Union (EU) and the unique legislation that has resulted from it.


As highlighted by the cases of ex-parte Brind and ex-parte Smith, UK courts are not bound to take unincorporated international law into account when reaching domestic decisions. One issue which must be borne in mind by the courts is the problem of introducing too wide a precedent for the use of international treaties in statutory interpretation and particularly because of the existence of so many ratified treaties on a multitude of topics. They can nonetheless be referred to, to resolve ambiguities in the common law. As highlighted by Lord Kerr, this is specifically “required” in human rights cases due to the prevalence of international instruments on the topic. This was concretely demonstrated in Hunter v Canary Wharf when Lord Cooke described the need to take account of Article 16 of the United Nations Convention on the Rights of the Child.


As mentioned above, one of the most significant examples of this is the ECHR, which was given direct effect through the HRA. It meant that ECHR rights formally became part of UK national law and domestically enforceable. It also had the effect of drawing ECHR case law into UK jurisprudence which, has itself, been influenced by many sources. This has led to the intriguing situation shown by the case of T and V v United Kingdom when the Court used the Beijing Rules to consider the right to privacy of juvenile offenders. As the UK had not even ratified these Rules, it highlighted how the UK’s decision to give direct effect to the ECHR has effectively given direct effect to its other sources also.


EU was directly incorporated into the UK legal system through the European Communities Act 1972. However, the most transformative of the EU’s legal principles have not been developed through EU treaty law, but through the case-law of the European Court of Justice. These include the supremacy of EU law, the principle of direct effect, and the principle of indirect effect and have had an unprecedented impact on UK courts and the decisions they have made. This was seen in the case of Factortame where the House of Lords were obliged by EU law to issue an injunction against the Crown and require the disapplication of the Merchant Shipping Act.

It could be argued that the interpretative effect of EU law goes too far beyond even that of the HRA. This was seen in Pickstone v Freemans where Lord Templeman argued that Community law required the imposition of additional words into section 1(2)(c) of the Equal Pay Act 1970. This thus throws up questions as to the effects that such substantive changes have had on UK laws and the extent to which international treaties should change UK jurisprudence. While the protections of human rights should arguably be buttressed at all international and domestic levels, legal discussions beyond Brexit will become increasingly important to determine where to draw the line.