Lord Myners was commissioned by the board to review governance at Nisa in the wake of a series of damaging headlines about the Scunthorpe-based business.
In his findings, he said: “There have been the obvious costs of high-profile leaks, expensive investigations and the sudden departure of board directors and executives.
“There have also been the less obvious, but still real, costs of slow and uninformed decision making, a confused strategy and weak financial discipline.
“Performance has been weakening and, at the same time, the market place has become more and more competitive.”
The former City minister said the group’s governance structures require fundamental change, “and quickly”, as they are eroding the performance of the business and benefits of membership.
Lord Myners called for a change of behaviours among the executive, the employees, the board and the members to bring an end to “the current climate of distrust and hostility”.
Christopher Baker, chairman of Nisa Retail Limited, welcomed the report and said the board needs to engage with members before reaching a conclusion on how to address its recommendations. CEO Neil Turton quit in September.