John Stewart, the newly appointed chief executive of National Australia Bank group, has tapped rivals Commonwealth Bank and Citigroup to reinforce senior management in the wake of the currency trading scandal that hit the bank in January.

Michael Ullmer, the former group executive in charge of institutional and business services at Commonwealth, becomes NAB's group chief financial officer, replacing Richard McKinnon. McKinnon had "decided to stand aside as part of the change process" following the scandal, according to a spokesperson for the bank.