The lawsuit emerged amid criticisms of the Thai Rak Thai government's lack of measures to prevent conflicts of interest involved with the privatisation of state enterprises. Government critics have likened these conflicts to unfair treatment of the public.

Veera Somkwamkhid, chairman of the People's Rights and Liberty Protection Group, filed the suit yesterday with the Crime Suppression Division.

In his filing, he accused Viset and Manoo Leophairote of breaking articles 12 and 18 of the Corporatisation Act, which bars those involved in preparing the privatisation of state enterprises from holding shares in the state enterprises for three years after they go public. He included 17 pieces of evidence allegedly implicating Veera.

"Although the prohibition does not cover top executives of state enterprises, Viset cannot avoid coming under the law," Veera said.

Both Manoo and Viset were members of the committee that prepared the transformation of the Petroleum Authority of Thailand into PTT Plc.

Anont Sirisangthaksin, senior executive vice president of PTT, however insisted that both men's stakes were legal. "Under the articles, those who cannot hold shares are only experts who serve on the committee," he said.

Veera said that Viset, then governor of PTT, was on the committee preparing and supervising the privatisation, as well as the related fund-raising scheme. Under the law, Viset should not have held shares in PTT for three years after the privatisation, or from October 1, 2001, when the agency was registered as a public company.

He referred to a document from the Commerce Ministry's commercial registration department showing that Viset was on a list of PTT shareholders as of April 9, 2004, when the three-year silent period had not yet expired. At that stage, Viset held 40,435 shares in the agency.

Veera said that Manoo, who chaired the privatisation preparation committee, was named as a shareholder in PTT annual reports between 2001 and 2003.

Manoo bought 30,000 PTT shares at Bt69 apiece on July 10, 2003, Veera said. Later, he bought two more portions, 30,000 shares at Bt69 apiece on July 23 and 20,000 shares at Bt68 on July 28.

Like other energy companies, PTT Plc has benefited hugely from the sharp rise in oil prices. Its share price has moved up to end yesterday at Bt268, an 18.6-per-cent increase from Bt226 at the end of 2005.

"Manoo's share-acquisition reports were filed with the Securities and Exchange Commission," Veera said. "The acquisitions confirm that he violated both articles of the law."

Conflicts of interest are also an issue being weighed by the Federation of Consumers Organisations in its plan to file a petition this month to nullify the privatisation of PTT.

The organisations were encouraged in their actions by a ruling by the Supreme Administrative Court in March that nullified two decrees supporting the privatisation of the Electricity Generating Authority of Thailand, due partly to conflicts of interest.

In that particular case, Olarn Chaiprawat was held up as a culprit.

The nullification brought Egat Plc back to its original status as a state enterprise.