Britain's Financial Services Authority (FSA), will force hedge funds and other investors who use derivatives to build large stakes in companies to follow the same disclosure rules as shareholders.

In its second new rule in a month the FSA requires that long positions that use so-called contracts for difference must be included and made public when holdings reach 3 percent or more. These instruments, known as CFDs, account for about 30 percent of electronic trading on the London Stock Exchange.

Last month the FSA enacted a new rule that forces investors to disclose short positions of more than 0.25 percent in companies involved in rights offers.

The new rules are aimed to increase transparency.