The opposition singled out Prime Minister Yingluck Shinawatra on the second day of the no-confidence debate yesterday.
Ms Yingluck was lambasted over alleged irregularities in the rice pledging scheme and flood response budget, and for failing to enforce anti-corruption laws.
The Democrat Party tried in vain to prevent other ministers from fielding questions on Ms Yingluck's behalf, particularly those concerning the controversial rice pledging scheme.
The opposition did not file a censure motion against Commerce Minister Boonsong Teriyapirom, who directly oversees the rice scheme, but chose instead to grill the prime minister, who chairs the national rice policy committee.
Ms Yingluck was criticised for relying heavily on scripted responses prepared by her aides to answer questions during the debate.
Deputy House Speaker Charoen Chankomol eventually decided that Ms Yingluck, as government leader, must answer for herself. If there were details that needed to be explained, she could ask ministers to provide them.
Ms Yingluck spent almost an hour responding to opposition leader Abhisit Vejjajiva, though the opposition criticised her for failing to adequately answer the questions. They said her responses sought only to promote the government.
Mr Abhisit said the government was making efforts to shield Ms Yingluck from political attack by preventing her from expressing her political views.
He said the rice pledging scheme is causing considerable damage to the country. It had led to a monopolisation of the industry, destroyed normal market mechanisms, and encouraged corruption, he added.
Even the National Anti-Corruption Commission (NACC) had warned the prime minister that the scheme could lead to corruption, Mr Abhisit said.
If the project continues, he said it would cost the government 224 billion baht a year, or about 10% of the budget. This would push public debt past 60% of GDP, he said, which is unsustainable.
He questioned how the government would be able to make a profit from exporting pledged rice _ the rice is purchased at above-market rates, making it impossible for traders to compete on the global market. It cannot sell the rice at a loss, as that would breach World Trade Organisation regulations.
As a result, Thailand has lost its position as the world's top rice exporter, Mr Abhisit said. Rice exports have tumbled by 25% since the rice pledging project started.
Mr Abhisit said the government should scrap the scheme so Thai rice can compete with that of international rivals.
Mr Abhisit said the scheme had tempted farmers to grow rice faster and in larger quantities, with quality deteriorating. He also questioned the release of rice from government stockpiles, which he said has been shrouded in mystery. Official sales figures have been scant, he said.
The project has now cost the state more than 200 billion baht. Only half of that has gone to farmers while the rest has been pocketed by corrupt politicians, rice millers and merchants, he claimed.
Ms Yingluck claimed the rice pledging scheme would lead to an 8% increase in the price of rice by the end of next year.
She said the government would try to prevent corruption in the scheme.
She also cited poll results which indicated most people were satisfied with the project. She admitted rice exports had slipped to third after Vietnam and India in terms of quantity, but claimed Thai export value was still number one.
Switching his attack to the government's flood prevention project, Mr Abhisit said the government had failed to comply with NACC regulations which stipulate that median prices for state procurement projects must be made public.
Ms Yingluck said the government recognised the importance of preventing graft. Still, it did not agree the NACC has the authority to order the cabinet to announce criteria for setting median prices.