A man claims he has been "deceived" by the NSW Trustee and Guardian (NSWTG) after his elderly mother's will was allegedly changed without his knowledge.

Key points: James Prentice claims his elderly mother's will was changed by the NSW Trustee and Guardian without his knowledge

James Prentice claims his elderly mother's will was changed by the NSW Trustee and Guardian without his knowledge He says his mother would have been incapable of understanding the fee structure when it was presented to her

He says his mother would have been incapable of understanding the fee structure when it was presented to her The law firm representing Mr Prentice has called for a parliamentary inquiry into the state body

James Prentice has launched legal action against the NSWTG to have it renounce its position as executor to his mother's will.

Mr Prentice said he was not aware that he was removed as executor to the will or of the costs associated with using the NSWTG, until after his 91-year-old mother died in June.

"We got handed this brochure with all of the charges applicable that mum never had, that we never had," Mr Prentice said.

"In 2016, mum was taken into this room in a very difficult state — nobody else was with her.

"We don't know what was said, we don't know what she was presented with.

"She would have been absolutely incapable of understanding any structure of fees, even if it was handed to her at the time."

Mr Prentice admits he did not request details of the fees and charges when the will was drawn up or in the years following.

"No we didn't, because we trusted them," he said.

"We trusted that they would do the right thing, that they would let you know, that they would disclose, that they would give you all of the information that you required to make an assessment at that point.

"I think it's hardcore deceit."

The Queensland-based law firm representing Mr Prentice has called for a parliamentary inquiry into the NSW Trustee and Guardian.

"There needs to be an overhaul of the system because it's currently not adequate," Attwood Marshall Lawyers senior associate Lucy McPherson said.

"It should be a requirement of the NSWTG — just as it is a requirement of solicitors — to make adequate disclosure when those documents are created.

"We're not saying that the NSWTG needs to be wiped out, but we consider that there have been some serious instances of malpractice within the body that need to be investigated."

Complicated fee structure

Ms McPherson claims the state body has a history of taking advantage of some of the most vulnerable people, including those with a disability.

Senior associate lawyer Lucy McPherson is calling for a review of the NSW Trustee and Guardian. ( Supplied )

"Not only in instances of deceased estates, but also particularly in scenarios where the NSWTG is acting as financial manager or trustee for somebody who has a disability and is unable to make decisions for themselves," she said.

Mr Prentice alleged he was charged $24,000 to execute his mother's will, calculated on a percentage basis according to the value of her estate.

Ms McPherson said the private sector had its fees capped and would have only been allowed to charge $5,636 to provide the same service.

"As you can see, [there is] quite a significant difference, but in [Mr Prentice's] matter, the estate assets are quite simple, it's not a complex estate, and it certainly doesn't warrant a $24,000 bill," she said.

"It's not a straightforward calculation; there are a number of different fees that are charged in different scenarios.

"Based on the medical evidence that we have about James's mother's capacity at that time, I have grave concerns that she had the capacity to understand the complicated nature of the fee structure."

Investigation underway

The NSWTG currently manages or oversees the financial affairs of approximately 16,000 people in the state.

Attorney-General Mark Speakman said Mr Prentice's matter was being investigated.

"I expect the NSWTG to address the allegations and to ensure that its practices meet community expectations," he said.

NSWTG spokeswoman Megan Osborne said all fees and information were discussed with clients at the time an appointment was made.

"When the customer comes in for their appointment, the will-maker, at the beginning of the interview, takes the customer through what the fees are for NSWTG to administer the estate," she said.

"NSWTG's current fees and commission were approved by the NSW Government and were based on recommendations made in the Independent Pricing and Regulatory Tribunal's review of fees of the NSWTG (2014).

"NSWTG has a fee-waiver policy which allows fees to be reduced or waived where they would cause hardship or are inequitable."