The Common Law Rules

In traditional common law jurisprudence, a large degree of consensus has emerged about the rules regarding the use of both conventional and customary international law before domestic tribunals.

A. Customary International Law

From the end of the eighteenth century, customary international law has been considered part of the law of the land. William Blackstone, in his Commentaries on the Laws of England, wrote that the �law of nations [customary international law] is here adopted in its full extent by the common law, and is held to be part of the law of the land.’^[489]

However, several qualifications are necessary to Blackstone’s broad, monist statement. Firstly, the existence of the customary rule relied upon must be strictly proved.^[490] Secondly, the customary rule must be either universally recognized by states around the globe or accepted as a binding customary rule by the state concerned.^[491] Thirdly, the applicability of rules of customary international law in the domestic legal order is subject to the overriding effect of statute law and, with one exception,^[492] that of binding judicial precedent.^[493] These latter limitations are fundamental. If an existing, unambiguous statute or binding judicial precedent is applicable, then the court must uphold that domestic law, regardless of whether it is compatible with the state’s international legal obligations.^[494] Finally, it is important to notice that when customary international law becomes part of the law of the land it changes and literally becomes domestic law, or the common law.

B. International Treaty Obligations

The second firmly accepted rule in this area is that international treaties have no binding force in domestic law without transformation.^[495] Treaties do, of course, create binding obligations for States Parties at the international level once they have entered into force.

The act of converting an international treaty obligation into a domestic statutory one is most often called �transformation’ or �incorporation.’ Statutes that perform this role may do by indirect enactment of the treaty - by specifying that the entire treaty is, or sections of the treaty are, to have the force of law in the domestic legal system (and then in many cases attaching the relevant treaty text as a schedule to the act).^[496] But they can also transform a treaty directly, by drafting a statute for the specific purpose of incorporating the international legal obligations within the precise language of domestic statutory provisions.^[497] This latter approach is in many ways preferable, because it allows the international legal obligations to be tailored to the specific statutory language of domestic legislation; but it has the drawback of decreasing the potential for uniformity in the application of the treaty around the globe.^[498]

Transformation is important because it ensures that Parliament remains the branch of government that makes law. Parliament creates legal rights and duties in domestic law through statutory enactment, not the executive or judiciary. Transformation also has the effect of making international law into domestic law: it completely changes its legal nature and ceases to be international law. As a result, domestic courts never actually apply international treaty law; they apply domestic legislation which contains rights and obligations that mirror those contained in the treaty.^[499]

In sum, under the common law, treaties have no binding force in domestic law without transformation by Parliament; and even after transformation the binding right or obligation, strictly speaking, is one of domestic, not international, law.

C.

The final set of rules regarding the use of international law in the domestic forum is that regarding the effect of treaties which have not been transformed, often referred to as �unincorporated treaties.’ Such unincorporated treaties have no binding force in domestic law, but in some cases may be used for the limited purpose of interpreting unclear domestic legislation.

This interpretive use is founded upon the rebuttable presumption that Parliament does not intend to legislate in violation of the state’s international obligations.^[500] This presumption is rebuttable and is subject to any available counter presumptions.^[501] Further, the rebuttable presumption does not even arise unless the court has failed to determine the meaning of the legislation through the application of ordinary principles of statutory interpretation. Thus, if the law is clear, domestic courts must apply it regardless of whether this will entail the breach of an international treaty. This is because it is fully within the sovereign power of the state to both enter into, and breach, treaty obligations: �the sovereign power of the Queen in Parliament extends to breaking treaties.’^[502]

In this context, the requirement for lack of clarity of domestic legislation has emerged as a precise one under the common law. The question of whether a provision is �unclear’ or �ambiguous’ only arises where that provision can yield at least two meanings, one which conforms to, and one which conflicts with, the international legal obligation.^[503]

If a domestic tribunal finds such an �ambiguity,’ the result is striking. The judge is empowered to look at the unincorporated treaty and in most cases, as a result of the presumption, will uphold the interpretation that complies with the international obligation. The presumption is so strong that it may even be applicable �retroactively,’ allowing a court to interpret a statute created long before the state became a party to the treaty, with the text of the later treaty.

This principle is obviously at its strongest when it appears that the domestic law was passed to give effect to an international obligation or may otherwise be assumed to have been drafted with the treaty in mind. Its application to laws which existed before the treaty is more difficult to justify as an exercise in construction but their Lordships are willing to proceed on the hypothesis that the principle requires one to construe the Constitution and other contemporary legislation in the light of treaties which the government afterwards concluded.^[504]

Therefore, legislation enacted in the 1960s may be interpreted in the light of a treaty to which the state only became a party in the 1980s. Such a broad temporal application of the ambiguity rule may be justified by the �always speaking’ rule of statutory interpretation.^[505]

This was the status of the common law rules regarding the use of international law before domestic tribunals for both the United Kingdom and the Commonwealth Caribbean until the early 1990s. From that period, however, the jurisprudence of the Privy Council started to diverge from that of the House of Lords in a series of death penalty cases. The fact that the House of Lords continued to apply the common law rules in their traditional form in the United Kingdom is noteworthy, especially considering that the same judges served on both judicial bodies.^[506]

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