* Ordinary Greeks angered by flagging anti-corruption drive
* Spaniards join protests before Greek parliament
* IMF, EU, ECB officials checking Greek budget figures
By Angeliki Koutantou
ATHENS, May 29 (Reuters) - Tens of thousands of Greeks vented their anger at the nation’s political classes in Athens on Sunday, staging the biggest in a week of protests as the government seeks backing for yet more austerity.
The huge crowd packed Syntagma Square in front of the Greek parliament, booing, whistling and chanting “Thieves! Thieves” as they pointed at the assembly building.
“We’ve had enough. Politicians are making fools of us. If things stay as they are, our future will be very bleak,” said a 22-year-old student who gave his name as Nikos.
Unlike the violent protests last year when radicals clashed with police, the peaceful crowds on Sunday were made up of ordinary Greeks, some of whom brought along their children.
Greeks are angry no politicians have been punished for the corruption they blame for the crisis, as well as the dire state of the economy and waves of austerity demanded under the terms of a 110 billion euro ($157.5 billion) bailout from the European Union and IMF last year.
Greeks have been protesting on Syntagma Square for five days, fired up by similar demonstrations across Spain. They were joined on Sunday night by a small group of Spaniards who had come to show their solidarity, raising banners in Spanish.
Spain has not had to seek an international bailout, unlike Greece, Ireland and Portugal, but it also faces major budget problems, lack of confidence in its debt, and demand for reform.
Police put Sunday’s crowd at 30,000 although the protesters, who have few formal leaders and are prompted by Facebook, say official figures usually underestimate the size of demonstrations by a wide margin.
Before the Syntagma Square rallies began, some Spanish protesters had accused Greeks of being too passive.
But on Sunday Ifigenia Argyrou, a 57-year-old insurance consultant, said all that had changed.
“People were indignant but they needed a motivation to express that. The Spanish people gave us that motivation,” she told Reuters. “We are not sleeping, we are awake. The IMF should get out. There are other solutions without them.”
Officials from the International Monetary Fund, EU and European Central Bank are in Athens checking Greece’s fiscal progress to approve a 12 billion euro aid tranche -- the fifth under the current bailout -- and possibly new funding the country needs to avoid debt default.
In return, the EU wants Athens to impose yet more austerity and reform, including privatisations.
Prime Minister George Papandreou’s PASOK has a comfortable majority in parliament but one weekend opinion poll showed it had lost its lead for the first time since it won elections in 2009. [ID:nLDE74R0BW] (Editing by David Stamp and Maria Golovnina)