German foreign minister Guido Westerwelle on Sunday (12 August) became the latest in a line of politicians calling for a referendum on handing over more powers to Brussels as part of a new EU constitution.

"I hope that we have a real European constitution and that there will also be a referendum on it," he told the Sunday edition of Germany's biggest-circulation newspaper, Bild.

The idea to hold a referendum on what Chancellor Angela Merkel sees as the only way out of the crisis - the formation of a true "political union" - has gained momentum in Germany.

"We need a political union. That means we have to give up further competencies to Europe, step by step, in an ongoing process," she told ARD public television earlier this month.

Politicians both in the ruling coalition and in the opposition in recent weeks have said this is the only way to legitimise new transfers of power to EU institutions, which would go beyond what the current German constitution allows.

German finance minister Wolfgang Schauble, from Merkel's own Christian-Democratic Union was the first to float the idea in June. He was followed by Bavarian Conservatives and now members of the liberal Free Democratic Party, Merkel's junior coalition member.

For his part, Horst Seehofer, the leader of the Bavarian sister party to Merkel's CDU, on Sunday also said in an interview with Welt am Sonntag that there are "three [legal] areas where one must ask the German people about it [power transfers]."

Meanwhile, the leader of the centre-left SPD party, Sigmar Gabriel, last week said the only way out of the crisis is to pool debt and sovereignty.

He also endorsed a recent essay written by German philosopher Jurgen Habermas along with an economist and another SPD member, which called for a referendum and for giving the European Parliament more powers so that there is no "taxation without representation."

Leading German magazine Spiegel Online has outlined forward three scenarios for a possible referendum.

It said one option is a voluntary poll on changing the German charter. A second scenario is a referendum forced by German ratification of a new EU treaty on power transfers, while a final option is a pan-European referendum on EU treaty changes.

The German Constitutional Court in Karlsruhe is due to rule on 12 September on the legal compatibility with German law of the European pact on budget discipline - the "fiscal compact" - and the eurozone's permanent bailout fund, the European Stability Mechanism.

In line with previous rulings, it is likely to ask for a bigger say for the German Parliament and point to the limits of the current German constitution as part of the eurozone architecture-in-the-making.