The Public Advocate says the merger threatens the reputation of the guardians unit at a time when two former staff of the Trustee's office are accused of a fraud, and also threatens the care of Canberra's most vulnerable people. The trustees manage people's finances and the guardians advocate for disadvantaged members of the public in medical, housing and other life decisions.

Although the merger won't happen until early next year, the government has already appointed the head of the Public Trustee's office, Andrew Taylor, as Public Advocate – making him in charge of the guardians unit as well. Mr Taylor is one of the few people involved understood to support the merger.

But former head of the public guardians, Heather McGregor, said it would be "a travesty" to give the guardianship function to the Public Trustee.

"This would be such a backward step for our most vulnerable citizens," she said in a submission to the government.

"The expertise required to properly fulfil a public guardianship function is quite different to the expertise of a financial manager. As well, there is a safeguard involved in the two roles being separate and independent.

"The potential for exploitation and abuse of the most vulnerable would be so much greater with the two statutory roles being combined."

The guardians unit also hit out at the plan, saying it had "profound concerns" and an "acute philosophical and ethical antipathy" to the move.

The two offices should be "aggressively separated" the guardians said, and merging them was not only out of step with the way things were done nationally and internationally but it risked the perception that care decisions were made on financial grounds.

The proposal demonstrated a profound lack of understanding of their role, the guardians said. They were appointed as a guardians of last resort when no one else in the person's life was able to take on the job, and worked with the most vulnerable and isolated people who were sometimes in conflict with their families.

But Mr Taylor said it would bring better coordination and reduce the "capacity for discord between the outcomes of the two roles of guardianship and management".

"Whilst I accept that there are philosophical differences in perspectives, skills and approaches taken by guardians and financial managers, it is reasonable for the community to expect that these services be delivered in a holistic manner," he said.

More than 130 people had both a guardian and a financial manager, he said, and having one agency do both jobs would "generate efficiencies allowing a represented person to deal with one agency, having consistent decisions made for them". It would also open up the possibility of charging for guardianship services. "There are many persons for whom management and guardianship services are provided that can afford and should pay for both services," he said.

The merger had "many benefits and few insurmountable risks", he said.

Human Rights and Discrimination Commissioner Helen Watchirs said there was a fundamental difference in the two roles.

"Having two sets of appointed and often involuntary decision-makers ensures that no single body is responsible for the entirety of a vulnerable person's life, ie financial as well as personal affairs – accommodation, health, living conditions, etcetera," she said.

The ACT Bar Association welcomed a single office for people to access both services however, but said: "a culture ought not be developed whereby the financial management considerations of the trustee function drive the broader-ranging considerations of the guardianship function".

President of the Law Society of the ACT, Martin Hockridge, warned that "the overriding view in the Public Trustee is financial and it is possible that someone wishing to assist, and giving priority to the financial aspect, may adversely impact a person's living arrangements."

An anonymous submitter said a close family member whose finances were managed by the Public Trustee had had more than $1000 taken from his bank account under the fraud uncovered last year that seriously shook confidence in the office. They continued that at the moment the guardians could provide independent scrutiny of payments, but if the two offices were merged that oversight would be lost.