@Walter Hinteler,
I'm well aware that the UK rejected membership in the Eurozone and retained its own currency.
The several overlapping treaty organizations addressing political union; travel and the movement of people within the organization and finally the EURO -- each with slightly different combinations of member states, together comprise the basic structure of the European Union. The specific issues currently driving discord within the EU variously involve all three of these structures. The contemporary political issues that result, involving tensions between national and EU governing bodies and among the member nations themselves tend to embrace all three.
That a treaty establishing the EU and its internal market is hardly news to anyone. Neither is it significant to the issues at hand. Instead it is the lack of democratic process and autonomy among member states that appears to be behind most of the internal issues the EU faces now.