EY's independence has once again been called into question after revelations it carried out an independent prudential report for NAB while also collecting $20 million as the bank's external auditor.

EY, formerly known as Ernst & Young, prepared the statutory report about NAB's risk management function last year and, at the behest of NAB's leaders, toned down the language in the final version of the assessment, according to a report in The Sydney Morning Herald and The Age.