Relationship between International Law and Municipal Law — Public International Law Notes

Relationship between International Law and Municipal Law

In 1977 the English Court of Appeal had to decide, in Trendtex Trading v. Central Bank of Nigeria (1977), whether a new rule of customary international law (that a State trading commercially loses its immunity) was already part of English law without any Act of Parliament. Lord Denning said yes — custom flows into the common law automatically, moving with the times. But when the House of Lords faced a treaty in the International Tin Council case (J.H. Rayner v. Dept of Trade, 1989–90), the answer was the opposite: a treaty changes nothing in English law until Parliament passes a statute. That split — custom in automatically, treaties only by statute — is the British practice, and it is the examiner’s favourite illustration.

One law or two? — the two theories, then what States actually do

The question is simple: when international law and a country’s own (municipal) law meet, are they one legal system or two? And if an international rule conflicts with a domestic statute, which wins inside the national court? There are two rival theories.

A. Monism

Monism (Kelsen, Lauterpacht) says international law and municipal law are one single legal order, with international law generally superior. On this view an international rule is directly part of national law and can be applied by national courts without any transforming legislation. The individual is the ultimate subject of both.

B. Dualism (pluralism)

Dualism (Triepel, Anzilotti) says they are two separate and independent legal systems — different sources (State will vs the common will of States), different subjects (individuals vs States), different substance. Because they are separate, an international rule has no force inside national law until it is “transformed” into national law by the State (usually by statute). Until then it binds the State internationally but gives the citizen nothing in the domestic court.

The difference matters in exactly one situation: can a private person rely on an un-transformed treaty in a national court? Monism says yes; dualism says no.

C. What States actually do — British practice

British (and largely Indian) practice is dualist for treaties, monist for custom:

Customary international law is incorporated automatically — it is treated as part of the common law and applied by courts without legislation, provided it is not inconsistent with an Act of Parliament or a binding precedent (the doctrine of incorporation; Trendtex, 1977; West Rand Gold Mining, 1905).
Treaties must be transformed — a treaty signed by the Crown has no effect in domestic law until Parliament enacts it, because treaty-making is executive but law-making is Parliament’s (the doctrine of transformation; the International Tin Council case / J.H. Rayner (Mincing Lane) Ltd v. Dept of Trade (HL, 1989–90); Maclaine Watson). This protects the citizen: the executive cannot change the law affecting his rights by signing a treaty behind Parliament’s back.

D. India’s practice

India follows the same broad pattern.

Article 51(c) of the Constitution is a Directive Principle: the State shall “endeavour to foster respect for international law and treaty obligations”. It is directory, not enforceable, but courts use it to read statutes in harmony with international law.
Article 253 empowers Parliament to make any law to implement a treaty, agreement or international decision — confirming that a treaty needs legislation to become enforceable domestic law.
Customary international law is treated as part of Indian law if not contrary to a statute (Gramophone Co. of India v. B.B. Pandey, 1984: “the comity of nations requires that rules of international law may be accommodated in the municipal law even without express legislative sanction provided they do not run into conflict with Acts of Parliament”).

Article 253, Constitution of India: “Parliament has power to make any law for the whole or any part of the territory of India for implementing any treaty, agreement or convention with any other country or countries or any decision made at any international conference, association or other body.”

In Simple Terms: In India a treaty by itself does not become law you can sue on — Parliament must pass a law to give it teeth (Art. 253). Article 51 only tells the State to respect international law; it is a goal, not a right a citizen can enforce. Custom, by contrast, is treated as already part of Indian law unless a statute says otherwise.

⚠️ DON’T CONFUSE — monism vs dualism (and incorporation vs transformation)

Monism = one legal order; international law applies directly, no legislation needed. Dualism = two separate orders; international law needs transformation into national law first. The matching techniques: incorporation (custom flows in automatically — the monist-style rule Britain uses for custom) vs transformation (a treaty must be enacted by statute — the dualist rule Britain uses for treaties). The trap is to say Britain is “monist” or “dualist” flatly. It is dualist for treaties, monist (incorporation) for custom — say both.

🧩 WORKED EXAMPLE — the Gleneagles Accord / un-transformed treaty problem

Facts. India is party to the Gleneagles Accord (a Commonwealth commitment against sporting links with apartheid). The Government lets two cricketers who played in apartheid “Bantuland” tour India. An NGO sues to stop them, relying directly on the Accord.

Rule. Dualism + India’s practice: a treaty/accord creates no enforceable domestic right until Parliament transforms it into law (Art. 253); Art. 51 is only directory.

Apply. The Accord binds India internationally but has not been enacted into Indian law. So the NGO cannot enforce it as a right in an Indian court; the courts can at most use Art. 51 to interpret existing law, not to create a new enforceable obligation.

Decoy. “It is an international commitment, so it must be directly enforceable at home.” That is the monist assumption — wrong for India’s dualist treaty practice.

Conclusion. Absent enabling legislation, the Accord is not directly enforceable; the challenge fails on that ground.

flowchart TD
    A["International Law vs Municipal Law"]
    A --> B["Monism<br/>one order; applies directly"]
    A --> C["Dualism<br/>two orders; needs transformation"]
    C --> D["British/Indian practice"]
    D --> E["Custom: incorporated automatically<br/>Trendtex 1977"]
    D --> F["Treaty: transformed by statute<br/>Tin Council 1989-90; Art. 253"]
    classDef box fill:#e8f0fe,stroke:#333,color:#111;
    class A,B,C,D,E,F box;

Case Laws

Trendtex Trading Corp. v. Central Bank of Nigeria (1977) — customary international law is incorporated into English common law automatically and moves with changes in custom (restrictive immunity adopted without statute).
J.H. Rayner (Mincing Lane) Ltd v. Dept of Trade and Industry — the International Tin Council case (HL, 1989–90) — an unincorporated treaty creates no rights or obligations in English municipal law; only Parliament can transform it.
West Rand Central Gold Mining Co. v. R. (1905) — custom is part of English law only so far as accepted and not inconsistent with statute (incorporation, qualified).
Gramophone Co. of India v. Birendra Bahadur Pandey (1984, SC) — rules of customary international law may be read into Indian law if not in conflict with an Act of Parliament.

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