Probably arguable, but according to Article 4 (2) of the Lisbon Treaty: [The EU] shall respect [Member States] essential State functions, including ensuring th

Probably arguable, but according to Article 4 (2) of the Lisbon Treaty: [The EU] shall respect [Member States] essential State functions, including ensuring the territorial integrity of the State, maintaining law and order and safeguarding national security. In particular, national security remains the sole responsibility of each Member State. The UK could insist that this is a national security measure.