The country’s biggest superannuation funds are risking the savings of millions of customers by spending their money in ways that do not have a clear benefit for retirees, the financial services regulator has warned.

The Australian Prudential Regulation Authority, in a letter to the sector, said super funds had “suboptimal” expense policies and displayed a “lack of rigour” when deciding to spend on sports sponsorships, travel, conferences and other payments to affiliated unions or employer groups.