The Court of Justice of the European Union has found in the case of C-165/16 Lounes that EU citizens who move to the UK and later naturalise as British retain their free movement rights under EU law even though they have become British. The court has held that the UK has wrongly been refusing to recognise free movement rights for such EU citizens since 2012.
The case has particular significance to those EU citizens who have naturalised as British following the Brexit referendum because it means that the UK has wrongly been denying them their EU law rights in the meantime. The victory is a Pyrrhic one for them, perhaps, because after Brexit these rights will be lost, unless the UK agrees that free movement law continues in some form, for example with a transitional deal.
The judgment does not just apply to EU citizens coming to the UK, though. It has considerable significance across the EU for the integration of long term residents from other EU countries.