Speaking as his countrymen went to the polls in a historic election, Papandreou said closer banking union was needed across the EU, but that it would be "catastrophic" for Greece if it had to leave the eurozone.

"I think we're at a make or break point in Europe," Papandreou, still the leader of the socialist Pasok party, told the BBC.

"We must leave behind all this nationalistic rhetoric about who's to blame, whether it's about the southerners or the austere Germans or whatever.

"We need to work together, we need to pool our strengths."

Papandreou said Greece was merely a harbinger of of the "deeper problems" in the European Union and the eurozone, particularly the lack of a banking union, common fiscal policy and common economic policy.

But he warned of the potential consequences of voting for parties that oppose Greece's bailout conditions and could force the country out of the eurozone, saying a "Grexit" could lead to a bank run and high inflation.

"This would be a major catastrophe and this would have not only social but also political consequences, which I believe will make it much more difficult for Greece to reform," he said.

Papandreou said there was also a risk that extreme political groups across Europe could profit from the crisis, after the neo-Nazi party Golden Dawn entered the Greek parliament in the inconclusive general election on May 6.

He said there was "ripe ground for populism, ripe ground for racist parties, neo-facist parties and extreme political views, which will not only in Greece but in other countries tear apart the fabric, the real values on which the European Union is based," he said.

Papandreou, who became prime minister in October 2009, was forced to resign late last year amid mounting discontent over the austerity measures he was trying to push through to help his country stave off bankruptcy.