New South Wales police begain their probe in April this year following allegations by a whistleblower of corrupt invoice payments made to executive events firm Human Group, a long-term supplier to the bank, that were approved by Rosemary Rogers, former chief of staff to NAB CEO Thorburn.

Rogers resigned from the bank in December last year. At the time, an email written by Thorburn to the bank's board was leaked to local paper The Australian, which referred to Rogers' departure and a "lapse of judgment".

With the police investigation in full swing, Fairfax Media reports the Human Group is now suspected of issuing invoices to NAB to make the bank cover the costs of Thorburn's trip to the luxury resort, where the rooms cost between $6000 and $45,000 per night, and a Thermomix worth about $2000.

The media agency says detectives are seeking information from NAB about if and when Thorburn reimbursed the Human Group, and the circumstances of the company's decision to pay for the holiday and kitchen appliance and whether there was any discount.

There is no suggestion that Thorburn is directly implicated in the fraud.

In a statement, NAB says: “NAB’s annual remuneration report, to be released today (Friday 16/11), states: 'Certain matters emerged in the course of an investigation into an alleged fraud on NAB by a former employee and supplier to NAB. These included certain control failings and breaches of policy in the Office of the CEO, and a small number of unintended breaches of policy by the Group CEO. These matters have been resolved and closed to the Board’s satisfaction'."