CA-2024-001773 - [2025] EWCA Civ 1057

Article 32

Supplementary means of interpretation

Recourse may be had to supplementary means of interpretation, including the preparatory work of the treaty and the circumstances of its conclusion, in order to confirm the meaning resulting from the application of article 31, or to determine the meaning when the interpretation according to article 31:

Leaves the meaning ambiguous or obscure; or

Leads to a result which is manifestly absurd or unreasonable.’

Put shortly, the aim of interpretation of a treaty is therefore to establish, by objective and rational means, the common intention which can be ascribed to the parties. That intention is ascertained by considering the ordinary meaning of the terms of the treaty in their context and in the light of the treaty’s object and purpose. Subsequent agreement as to the interpretation of the treaty, and subsequent practice which establishes agreement between the parties, are also to be taken into account, together with any relevant rules of international law which apply in the relations between the parties. Recourse may also be had to a broader range of references in order to confirm the meaning arrived at on that approach, or if that approach leaves the meaning ambiguous or obscure, or leads to a result which is manifestly absurd or unreasonable.”

I make two points consequent on that passage from Anson. First, at issue in this appeal are provisions of the Withdrawal Agreement dealing with citizens’ rights. Those provisions reflect the position as it was agreed by the UK, the EU and the Member States to apply reciprocally to EU citizens resident in the UK and British citizens resident in EU Member States. Further or additional measures implemented by the UK relating to EU citizens resident in the UK could not be “read into” the Withdrawal Agreement, because the treaty reflects the common intention of the parties which cannot be altered by one party acting alone. Secondly, I have already referred to two contemporaneous documents published by the UK government outlining the Government’s intentions in relation to EU nationals resident in the UK once the UK left the EU (see paragraphs 20-22 above). Those documents are amongst the “broader range of references” (cf Anson paragraph 56) to which this Court could potentially have regard to confirm the meaning of the Withdrawal Agreement or to resolve ambiguity, obscurity, absurdity or unreasonableness.