Western Sahara Campaign UK v Secretary of State for International Trade & Anor.

Section 9 of the Taxation (Cross-border) Trade Act 2018 empowers regulations giving effect to an international arrangement. It does not require the court, in reviewing the regulations, to determine the legality or ultimate international-law meaning of the underlying treaty where the domestic instrument mirrors its wording.

International treaty interpretation begins with the ordinary meaning of the text, read in context and in light of the treaty’s object and purpose. Supplementary international-law rules inform that exercise but do not authorise rewriting clear language. Section 28 requires regard to relevant international arrangements, not the whole corpus of customary international law. The claim was also non-justiciable under the foreign act of State doctrine, and no public-policy exception applied.

The claimant sought judicial review of two customs instruments made under section 9 of the Taxation (Cross-border) Trade Act 2018. The instruments implemented the United Kingdom–Morocco Association Agreement by extending preferential tariffs to products originating in Western Sahara subject to controls by Moroccan customs authorities.

The claimant argued that the Government had acted outside section 9 because the agreement, properly interpreted in light of international law, could not cover those products. It also alleged breach of the section 28 duty to have regard to relevant international arrangements. The court considered whether it was required to interpret the treaty, the applicable treaty-interpretation principles, customary international law concerning third parties and self-determination, justiciability, foreign act of State and State immunity.

1. Claim dismissed. The section 9 challenge failed because the Regulations reproduced the relevant treaty wording and therefore gave effect to the arrangement. Section 9 did not require the court to determine the underlying treaty’s legality or international-law meaning as a route to challenging the Government’s treaty-making decision, which was non-justiciable.
2. The domestic authorities established that international treaties may be considered where necessary to resolve ambiguity or obscurity in legislation. They did not create a general power to review or supervise the Government’s decision to conclude a treaty. Here there was no material ambiguity: the UKMAA and the Regulations covered goods originating in Western Sahara subject to controls by Moroccan customs authorities.
3. Had interpretation arisen, Article 31(1) of the Vienna Convention on the Law of Treaties required the ordinary meaning of the text to be read in context and in light of object and purpose. Article 31(3)(c) required relevant international-law rules to be taken into account, but supplemented rather than displaced the primary rule. Articles 53 and 71 did not authorise the interpolation of “lawful” or a rewriting of clear treaty language.
4. The court would not conclude that customary international law extended the pacta tertiis rule in Article 34 of the Vienna Convention to non-self-governing territories. Nor had the materials established that the right to self-determination, or the corollary right to permanent sovereignty over natural resources, was a peremptory norm. An erga omnes obligation was distinct from a peremptory norm.
5. The section 28 duty concerned relevant international arrangements. It did not require a general review of customary international law. The duty was focused on arrangements relevant to the particular statutory function and was in substance a “good housekeeping” provision intended to prevent inconsistency between arrangements.
6. The foreign act of State doctrine independently provided a further obstacle. The claim required adjudication on the alleged unlawfulness of Morocco’s conduct in relation to Western Sahara. The public-policy exception did not apply: the case was not a paradigm case involving a jus cogens breach, involved a general rule rather than an individual right, and the balance favoured comity. The proposed extension of State immunity was rejected as resting on a slender foundation.