A former National Australia Bank executive is expected to be charged with more than 50 offences relating to an alleged $40 million fraud, after handing herself in to police on Tuesday.

Rosemary Rogers was chief of staff to former NAB boss Andrew Thorburn and his predecessor Cameron Clyne.

Police will allege Ms Rogers received $6.6 million in corrupt commissions to continue a contract with an events management company and overpay their invoices.

Ms Rogers handed herself in to officers at Surry Hills Police Station at 11am on Tuesday.

In a statement, a NAB spokesperson said the bank was cooperating with police.

“The alleged fraud was reported by a whistleblower,” they said.

“NAB responded immediately, investigated and reported it to police.

“If the alleged fraud is proven, it represents a most serious breach of trust by a former employee.

“NAB is the victim in this matter. Police have confirmed that no one at NAB is under investigation, including former CEO Andrew Thorburn, and there is no suggestion of any wrongdoing by anyone at NAB.”

Mr Thorburn quit the NAB’s top job at the end of February amid the fallout from the banking royal commission.

Last week, NSW Police charged Helen Rosamond with 56 counts of bribing an agent and two counts of gaining benefit by deception amounting to $6 million.

Ms Rosamond is a director of events management company Human Group, a supplier to the bank for about 12 years.

Police allege the offending happened between 2013 and 2017.

NSW Police say they haven’t ruled out further arrests and the investigation is still ongoing.

In February last year, NSW Police started investigating allegations of corrupt commissions being paid for contracts with the bank.

Investigators allege the fraud amounted to about $40 million over five years.

-ABC