The latest UTCC survey found most businesses continued to pay kickbacks to state officials and politicians, in a range of 25-35% of the project value, despite growing campaigns for all parties to tackle the country's widespread corruption problem.
The UTCC's Corruption Situation Index (CSI) is based on 2,400 respondents in the business and government sectors, and the score was 39 points in December last year, down from 41 points in June. This level is regarded as critical, as above 40 is considered moderate. The closer a CSI score is to zero, the higher the level of corruption, while 100 shows high transparency and a lack of graft.
Thanavath Phonvichai, vice-president for research at the UTCC, said corruption last year was estimated to cost 240-330 billion baht, compared to the country's overall investment and procurement budget of 2.4 trillion baht.
Based on the UTCC's calculation, if corruption stands at 35% of the investment and procurement budget, it would cut the country's annual GDP by 2.63%.
Tea money is the most popular form of corruption, making up 30% of the estimated corruption value.
Mr Thanavath said there is information that in certain northern provinces the tea money is now as high as 50% of the value of the investment project.
"Corruption is now widespread both in government agencies and local administration organisations," he said, adding politicians are the major source of corruption followed by state officials and businesses.
Most respondents said the gravest area of concern was the government's controversial rice pledging scheme. Future concerns include the government's planned 2-trillion-baht infrastructure investment project and 350-billion-baht water management project.
Respondents said the most effective way to tackle corruption is to start with politicians, followed by state officials and businesses.
"We desperately need to speed up legislative reform to impose serious penalties for those engaged in corruption," he said. "The public and private sectors should play more of a role in participating in corruption inspections and informing the public once corrupt practices are found. It is also important for information on investment projects to be transparent."
The 2013 Corruption Perceptions Index compiled by the Berlin-based Transparency International rated Thailand at 102 out of 177 countries, down from 88 the previous year, meaning corruption in Thailand had worsened.