(Original post by scrotgrot)
Sovereignty is about jurisdiction. The EU only has a sort of jurisdiction over member states insofar as member states have voted to be members and to apply European directives in their own sovereign legislative jurisdictions.
The method of entry isn't particularly relevant: there are plenty of sovereign states that have voted themselves into membership of a larger state. As for applying directives - directives have to be implemented in domestic legislation. However other EU legislative instruments have
without the member-state's action: they become law not because of our parliament or government put them in place, but because the institutions of the European Union have declared them to be so within the law.
We can refuse to implement it if we want and there's nothing in law the EU can do to stop us - I'm not even aware of any legal (as opposed to fiscal or diplomatic) mechanism by which an intransigent member state could be kicked out or otherwise punished.
The EU does not have a police force, but neither does the British Government. Our police are operationally independent bodies, just as our courts are. The British courts, like the ECJ, are bound to implement British law. A court can apply an injunction to prevent a person or public authority acting outside of the law with criminal penalties: in doing so, they must recognise European law.
Where British law conflicts with EU law, it is clear that the courts are bound - where applicable - to strike down the relevant British law. This is not theoretical: we've already had the Factortame
cases. It was an English court that struck down the relevant parts of the Merchant Shipping Act 1988 when it was clear it conflicted with EU law.
I appreciate there's a big distinction between how the two operate, but ultimately what NYU2012 says about is correct: we have an established system for recognising what is law in this country, and EU law not only has effect here, in its defined areas of competence it is supreme over any legislation made by the UK Parliament.