Treaty

International law prescribes neither a fixed form for a treaty nor any fixed procedure for its conclusion. It may be concluded by an exchange of diplomatic notes incorporating an agreed-upon text signed by authorized officials or by the signing of one or more copies of the text by officials authorized to express the consent of their respective governments to be bound by the treaty. Many important treaties require ratification by each of the contracting parties. In such cases the negotiators, after reaching agreement on the final text, sign the document and then submit the proposed treaty for ratification to the constitutionally authorized authority, usually the head of the state or the head of government.

Treaties may be terminated in various ways. The treaty itself may provide for its termination at a specified time or it may allow one party to give notice of termination, effective either at the time of receipt or following the expiration of a specified period. A treaty may be terminated by one signatory's repudiation of its obligations; such a unilateral termination, however, may provoke retaliatory measures. A treaty may also be terminated by reliance on the rebus sic stantibus principle (Latin, “things remaining that way”), that is, when the state of affairs assumed by the signatory parties (when they signed the treaty, and therefore the real basis of the treaty), no longer exists, and a substantial change in conditions has taken place.

Rules of international law governing the conclusion, validity, effects, interpretation, modification, suspension, and termination of treaties were codified in the Vienna Convention on the Law of Treaties, adopted in 1969 at a conference convened by a resolution of the UN General Assembly. Representatives from 110 nations participated, including Great Britain, the United States, France, and most other United Nations members, as well as several non-members, including Switzerland. The draft was prepared by the International Law Commission. The convention came into force in January 1980 following ratification by 35 nations.

The power to conclude treaties rests with the Crown. This power is delegated to the executive, so government ministers can sign treaties without reference to Parliament. However, the treaty does not give rise to legal obligations in domestic law unless its provisions are expressly incorporated into national law by statute. One such example is the European Convention on Human Rights, to which Britain is a signatory, and which was incorporated into UK law by the Human Rights Act 1998.

The courts will examine treaties on the basis that Parliament cannot have intended to legislate in a way which conflicts with the country's treaty obligations; and, accordingly, if there is an ambiguity in a statute, the courts will take it to mean whatever best fits with the treaty. But if a statute is clear, the courts must enforce it even if it conflicts with the treaty.