HC Deb 25 February 1971 vol 812 c252W
Mr. Elystan Morgan

asked the Attorney-General whether he took into account the fact that the Treaty of Vienna has not been ratified by either the United Kingdom or the Republic of South Africa in formulating his advice on agreements between the two countries which would otherwise be governed thereby.

The Attorney-General

Yes. I also took account of the fact that the Vienna Convention on the Law of Treaties is not retrospective in its application. The paragraphs of Article 31 of the Convention reproduced in paragraph 13 of the Law Officers' Opinion (Cmnd. 4589) are, however, declaratory of customary international law and were cited in the Opinion as a convenient and concise statement of the relevant customary international law rules.