"The euro crisis is changing the shape of the EU. As the countries in the eurozone seek to strengthen it by centralising economic policy making, three tiers are emerging within the union. The countries committed to further integration may set up new institutions. (...) At the core of the new structure, the 17 eurozone countries will submit national budgets and some economic policies to the control of EU institutions. This first tier will probably – as France and Germany are proposing – have its own budget, separate from the EU budget, to help countries that suffer economic shocks or are introducing painful structural reforms. The eurozone will be steered by regular meetings of its finance ministers and heads of government. A new body of members of the European parliament from eurozone countries and national parliamentarians from those states is likely to hold leaders to account.
A second tier, consisting of countries that aspire to join the euro, is already known as "eurozone plus". This group, which includes Poland, will accept much of the same supervision of budgetary and economic policy as the first tier. It will also join eurozone members in the banking union, which will start with centralised supervision and later extend to deposit insurance and resolution regimes.
The third tier will consist of the UK and a few others that do not wish to give up any more economic sovereignty."
Charles Grant, "A three-tier EU puts single market at risk" (Financial Times, 26.10.2012).