Consequences for the UK
By paying attention to the doctrinal limits of European law to state discretion in this policy area, the anticipated consequences for the UK are that, during the interregnum phase, European law would still hold and it could possibly have an apres-coup effect on the formulation of domestic nationality law. Modifications to policies even within the domaine reserve may come to be scrutinised by the European Court of Justice.
In particular, if the UK passes reforms to its domestic nationality law, these would be subjected to judicial review by the European Court of Justice. The UK would be prevented from hardening its domestic nationality law with the aim to punish instrumental acquisition of multiple nationalities. More precisely, the UK cannot pass domestic nationality provisions easing naturalisation only for some EU citizens: It would violate the principle of equality or non-discrimination. The UK would also be prevented from passing domestic nationality provisions having the effect of barring, or rendering more difficult or overly onerous, naturalisation of second country nationals, since such a policy would violate the principle of legitimate expectations. It is not impossible that making applications for indefinite leave to remain harder would also be held to be at odds with this general principle of European law.
Furthermore, the UK would be prevented from fighting instrumental naturalisation of its own nationals. It could not strip instrumental natura- lisers of their British nationality and/or residence rights. It could be hard to prevent double residence for citizens with multiple nationalities. The UK might favour a return to the genuine link doctrine, developed by the Nottebohm-jurisprudence prevailing in international law, which considers citizenship to be ‘a social fact of attachment’21 to claim that, if the person has his/her habitual residence or other key interests in the UK, the ‘effective nationality’ is the British membership, and not the nationality of the member state the person also is a member of. European law, however, prevents the UK from requiring such citizens to have a ‘genuine link’ with it. Finally, the UK would probably not be allowed to raise fees in any significant way for British nationals wishing to renounce nationality with the purpose of becoming naturalised in other parts of the Union.
In general terms, it would be detrimental to negotiations to harden the UK nationality laws and/or immigration laws. It should not be excluded that it would be favourable to negotiations to move in the opposite direction, for example, providing for automatic transformation of permanent residence into indefinite leave to remain, allowing second country nationals to naturalise without being subjected to citizenship tests or disproportionate fees. No such political will has been expressed.