Statesman Prem Tinsulanonda continued his campaign against corruption on Saturday with a warning that the situation was not improving.
Gen Prem said corruption remained widespread in the country despite some signs of improvement in a widely quoted international survey.
"Corruption in our country remains high. We should be ashamed and embarrassed because we are a corrupt country," the Privy Council president told a forum held at parliament on the role of religion in the fight against corruption.
Thailand was ranked 76th out of 168 countries in the Corruption Perceptions Index by Transparency International last year, up dignificantly from 85th in 2014 and 102nd in 2013.
But the country's "cleanliness score" from Transparency International over the past three years has improved only slightly, from 35 out of 100 in 2013 to 38 in 2014 and last year.
Gen Prem said the score was an indicator which substantiated his view that the country was still bogged down with problems.
But the former prime minister said he was encouraged by the National Legislative Assembly, which hosted the event on Saturday, and other groups that were campaigning for better measures to clamp down on corruption.
Uprooting corruption must start in childhood as children must be taught that it is evil, he added.
However, Gen Prem refused to be drawn into commenting on a dispute that has flared between his former aide, Adm Pachun Tamprateep, and the Royal Thai Police Office (RTPO).
Adm Pachun made headlines when he posted a message online claiming that an army general was demanding money from police officers in exchange for their promotions.
The RTPO said the allegation — similar claims have been made countless times by other over m any decades — had hurt the image of the force and filed defamation and computer crimes charges against him.
Deputy Prime Minister Prawit Wongsuwon, who oversees the police force said the police were right to take action, but he has since softened his stand. He said perhaps the police should take into account Adm Pachun's intentions in posting his message.
Gen Prem, meanwhile, said he had no more to say on the issue.
Gen Prem has never made public his support for Adm Pachun but the retired navy officer said on Thursday when he reported to police to answer the charges that Gen Prem had given him moral support in his fight.
In any case, the row appeared set to end, especially after Prime Minister Prayut Chan-o-cha spoke out on Friday, saying he hoped cooler heads would prevail.