Triquet v Bath

Facts

• The defendant was a domestic servant of the Bavarian Minister (ambassador) in London
• He was arrested for a private debt
• He claimed diplomatic immunity, arguing that the privilege extended to the servants of diplomatic agents under the law of nations
• The plaintiff argued that without specific statutory authority, no such immunity existed in English law
• Lord Mansfield CJ presided

Issue

1. Whether customary international law on diplomatic immunity formed part of English domestic law and could be applied directly by English courts without a specific Act of Parliament.

Held

• Lord Mansfield held that the law of nations is part of the law of England
• Customary international law on diplomatic immunity is directly enforceable in English courts
• No specific statute is required for its application
• This establishes the incorporation doctrine (also called Blackstone's doctrine): customary international law is automatically part of the common law
• The servant was entitled to immunity from arrest

Ratio Decidendi

The law of nations, in its full extent, is part of the law of England. Whenever any question arises which is properly the object of the law of nations, it may be considered and decided upon the principles of that law. The privilege of foreign ministers and their servants is part of the law of nations and is therefore enforceable as part of English law without further legislative action.