Under Article 27 VCLT, INTERNAL LAW cannot be used by a State as a justification for FAILURE TO PERFORM A TREATY. This codifies the principle that:

1. Article 27 VCLT: 'A party may not invoke the provisions of its internal law as justification for its failure to perform a treaty. This rule is without prejudice to article 46.' 2. This codifies the PRINCIPLE OF SUPREMACY of international law over national law in the realm of treaty performance. 3. Article 46 VCLT recognises a narrow exception: a State may invoke a violation of its internal law of fundamental importance regarding competence to conclude treaties if the violation was MANIFEST. 4. The principle is reflected in the maxim 'pacta sunt servanda' (Article 26). 5. Hence option B is correct. _Source: UN Charter 1945 / Vienna Convention on Law of Treaties 1969 / Geneva Conventions 1949 / ICJ Statute / UDHR ICCPR ICESCR — Vienna Convention on the Law of Treaties 1969, Article 27_