Limits of Public International Law
A set of international norms pertains to the withdrawing of status civitatis as such. The power of states to determine its members is not unfettered. The decision to revoke nationality finds its limits in international norms in the form of treaties or customary law.8 Leading principles on loss of nationality can be found in the Articles 5-9 of the 1961 Convention on the Reduction of Statelessness and as well as the 1997 European Convention on Nationality. However, such instruments would not apply since Brexit would not cause statelessness. So what other sources are there?
Article 15 of the Universal Declaration on Human Rights states that ‘everyone has the right to a nationality,’ which may not be withdrawn arbitrarily. Although the Universal Declaration is not a binding instrument, the forbiddance of arbitrary deprivation is repeated in other treatises and instruments. ‘Deprivation,’ which domestically is an act of the administration, in this setting covers ex lege loss of nationality.9 An example of
such an arbitrary loss is, for example, a retroactive restriction of a ground 10
A first practical implication follows from here. The UK cannot, lest it violates international law, retroactively deprive second country nationals who have naturalised in the UK of their current status were it somehow to push for expulsion of ‘non-Brits’ altogether; nor can the UK retroactively deprive of British nationality citizens who, having the citizenship by birth of another EU member state, also naturalised in the UK. This is a first limit to the possibilities of the exiting state to protect itself against instrumental use of multiple citizenship.
Now all provisions on loss of citizenship need to be read in the light of the general principle of the UNDHR banning arbitrary deprivation. The Universal Declaration does not specify the exact circumstances under which one would have to conclude that there is an arbitrary withdrawal (Marescaux 1984) but some general principles follow from this obligation to avoid arbitrariness.11 These principles have to be observed not only if the loss or deprivation would cause statelessness, but in all cases where a person would be stripped of a citizenship. The Brexit loss provision would need to obey these principles.
An intriguing issue is whether the loss of Union citizenship entailed by Brexit might demonstrate arbitrary features in its being unchallengeable. The application of loss provisions must be possible to challenge in court, but in this scenario, it is unclear whether the principle would imply letting British citizens challenge the loss provision before an English court, before courts in member states where they are residing, or before the European Court of Justice. As we shall see there is a quite limited possibility that the European Court of Justice might be involved. Were this the case, the Brexit loss provision would comply with international law requirement on being challengeable. While it seems likely that some rights associated with Union citizenship could be upheld if deprivation of these was challenged, it is less clear if loss of the status as such could be challenged, let alone if it could be frozen for the British citizens concerned.