This paper analyses competing approaches to proof of foreign nationality in the British courts, in the context of challenges to deprivation of citizenship. I argue that prevalent British approaches to proof, as on display in the Pham litigation and subsequent cases, are in unproductive tension with a fundamental principle of nationality law, namely that it is for each state to determine under its law who are its nationals. Prevalent British approaches elide this principle, effectively wresting interpretive authority over foreign nationality law away from the relevant foreign state. I argue for approaches focused on direct ascertainment of foreign nationality, as opposed to its reconstruction according to British standards.

Rayner Thwaites, Proof of Foreign Nationality and Citizenship Deprivation Pham and Competing Approaches to Proof in the British Courts, Modern Law Review, 2022.