WARREN BUFFETT, the billionaire investor, lost a battle to keep one of his shareholdings secret yesterday after a watchdog dismissed his argument that the disclosure would cause a run-up in the price and spoil his investment strategy.

The chairman and chief executive of Berkshire Hathaway had appealed a decision by the US Securities and Exchange Commission, the regulator, in February to deny his request to keep the holding quiet for one year.

The SEC said: “Berkshire failed to demonstrate a likelihood of substantial competitive harm from the disclosure of its acquisition program.”

Mr Buffett, whose investment strategy is widely admired, told the SEC that disclosure of his acquisition strategy for a certain stock led other investors to mimic him and cause a rise in the price of the stock. The SEC said Berkshire had not supplied enough information: “Berkshire’s request appears over-broad.”

The argument’s validity rests on the size and brand of the stock — whether he is buying a blue-chip like IBM or a thinly traded stock of an experimental start-up. Matters such as the length of the acquisition period and other details can help the SEC to determine whether confidential treatment is appropriate.

Anyone who invests more than $100 million (£63 million) in US stocks must make a filing with the SEC to declare their stock holdings. Disclosure is considered good for investors who need to know, for example, if their money is being invested in a company with high-risk stakes, or morally objectionable practices. They can, however, apply to keep some holdings confidential if they can prove that it is in the public interest.

The application process is lengthy and cumbersome and ripe for manipulation by major investors who know how to play the system.

Despite his defeat, however, Mr Buffett can take the matter to the Federal Court, allowing him the option of keeping his holding secret for even longer.