Unlike the United States, Thailand has no law forcing nominees to disclose their shareholders' names, Sopawadee told reporters yesterday.

"We cannot force them to disclose their shareholders' names because of the lack of law. What we can do now is wait for information after listed companies close their new shareholders registration," she said.

Although TSD serves as a register of the country's listed companies, it cannot track who the real investors behind nominees are, she said.

"Corporate governance is beyond the law. Executives of companies with good corporate governance would not participate in stock manipulation," she said.

Chalee Chandanayingyong, assistant secretary-general of the Securities and Exchange Commission, said a nominee law was in the process of being drafted by the  watchdog's legal affairs team.

"The SEC would be circumspect in issuing a nominee regulation because it is a sensitive issue. Some investors don't want to reveal their names publicly. The SEC would have to balance the advantages and disadvantages," he said.

Meanwhile, a source in the brokerage community, said it was difficult to check who the real shareholders are because most big investors and politicians make transactions through nominees, which can be easily established domestically or internationally.

Buying a stake through nominees is periodically adopted to skirt laws mandating the start of tender offers after 25 per cent of a company's shares are purchased. No one knows if several nominees holding a sizeable stake in a listed company are from the same group, the source said.

"We have to accept that there are is an abundance of nominees in the Thai stock market and retail investors lose the advantage because they don't know who the real shareholders are. Foreign investors have paid attention to information disclosure, so the Thai stock market scored within the low range for corporate governance," the source said.