Which of course is false.
> The principle was derived from an interpretation of the European Court of Justice, which ruled that European law has priority over any contravening national law, including the constitution of a member state itself.
"The majority of national courts have generally recognized and accepted this principle, except for the part where European law outranks a member state's constitution. As a result, national constitutional courts have also reserved the right to review the conformity of EU law with national constitutional law"
And guess why and how they are able to do that - that's right, by retaining full sovereignty of their own justice systems. Even obeying rulings of the ECHR is purely a matter of courtesy more than anything, as neither EU nor ECHR have any enforcement mechanism beyond withholding funding, as many EU member states have proven time and time and time again.
I can't say what it takes in every country, but in Denmark the procedure is as follows :
- The proposed change must pass a vote in parliament.
- There must then be an election to parliament.
- The new parliament must also vote in favor of the proposed change.
- Finally a popular vote must pass with at least 40% of all eligble voters voting for it. If less than 40% of eligble voters vote (regardless of where they cast their vote), the proposition fails.
It probably goes without saying that changing the Danish constitution is not a task taken lightly. The Danish constitution also explicitly forbids giving up soverenity.
My impression is that the UK in particular has that problem. Other european countries take the more pragmatic and sane option of... simply ignoring the EU.