A former ASIC investigator is calling for the 'big four’ insurance companies to join the big banks in facing the Banking Royal Commission. 

The forensic investigator who spent 20 years at the watchdog says PwC, Deloitte, EY and KPMG are likely to have been pressured into approving reports for fear of compromising financial relationships.

Despite damning evidence, a recent interim report from the Royal Commission made no recommendations to the Federal Government, sparking Opposition calls for the Commission to be extended.