The Greek Prime Minister, George Papandreou has thrown into doubt the deal to tackle the eurozone debt crisis.
In an unexpected move, he has called a referendum on the measures agreed last week by European leaders. One analyst said a "no" vote by the Greeks would "bring the house of cards tumbling down".
Greek MEP Anni Podimata, who is also a member of Mr Papandreou's ruling Pasok party, told Today presenter John Humphrys that the referendum "intends to provoke a catharsis" within the country.
But the president of the Athens Chamber of Commerce, Constantine Michalos, condemned the move as "an act of political schizophrenia and political blackmail".
And he told the programme: "What's the point of a vote of confidence when he runs the risk of the people reversing the EU decision just a few weeks later?
"The financial markets are in the doldrums, the real economy has completely stagnated, and the euro stands threatened as a result of this gross act of irresponsibility and political mismanagement."
And the decision to hold a referendum had an immediate impact on the markets. The German stock index was down more than 4% in early trading, with a similar fall in France. And the FTSE 100 lost around around 3% of its value.
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