The senior businessman appointed by Prime Minister Tony Abbott to review Australia's renewable energy target has been the subject of a secret internal investigation into his role as a former director of a firm involved in Australia's worst foreign bribery scandal.

The investigation findings were sent earlier this month to the Reserve Bank board and deal with Dick Warburton and his fellow former Note Printing Australia directors' knowledge and handling of Note Printing Australia's sanctions-busting trip to Iraq in 1998.

On Monday, Mr Abbott personally approved the appointment of Mr Warburton to review the nation's renewable energy target, despite serious questions about the role of Mr Warburton and his fellow former NPA directors in overseeing a company that police allege engaged in repeated foreign bribery.

The federal police have alleged that during the period Mr Warburton was an NPA director, the company repeatedly engaged in foreign bribery across Asia.