Finanstilsynet, the Danish financial services authority, has launched a formal investigation into "closet indexers" - mutual funds that claim to be actively managed, but in reality charge high fees for index-like performance.

Finanstilsynet said in a report published Tuesday that it has analysed the performance of 188 fund-management departments, or teams, at Danish financial services groups, and found 56 of them that "are not giving consumers the active management that they pay for".