It's where there is a vegetable garden he likes to look at and where there is a big backyard where he likes to pace. The pacing makes him feel secure and reduces his anxiety.

Marcus is 45 and has autism and an intellectual disability.

His mother, Sherry McArdle-English, says that sense of security and safety in his home of 21 years is now under threat due to the intransigence of the National Disability Insurance Agency and a shift away from "people-centred care" in the disability sector.

"The federal government created the NDIS system to support and care for those vulnerable through disability. What has happened?" she said.

The three-bedroom ACT government house in which Marcus lives has a bedroom each for two clients and another for a support worker. The problems started when the second client moved out for family reasons.

The ACT-based provider Livability Australia says the NDIS firstly wouldn't cover the funding shortfall until a new housemate was found, leaving it to cover the gap since May.

When Livability Australia did find a suitable housemate, with similar needs to Marcus, the NDIS deemed they were not eligible for the funding level that would allow them to go into the house.

In other words, the new potential housemate was only allowed to live in a house where there were three clients to one support worker; not two clients to one support worker.

That leaves Marcus in limbo without a housemate, his mother and Livability Australia paying more to keep him in his long-time home and Marcus going downhill emotionally and withdrawing socially because his routine and structure have been changed.

Ms McArdle-English, a long-time disability advocate in the ACT, says if she has been stonewalled by NDIS staff and feels if she can't get answers, the average person has no hope.

"NDIS staff appear to be unapproachable," she said.

"Although the wellbeing and safety of clients is at risk, the NDIS staffing mandate is set at 'lower costs'. We need to ask, 'At what cost to the individual client'?"

Marcus could move to a bigger share house. But that shouldn't be the answer, his mother says, and would most likely cause him harm.

"What Marcus needs is familiarity and consistency," she said.

Ms McArdle-English said she was also working from the premise people with disabilities such as her son would receive the same level care they had always received, long before the NDIS was introduced.

She said this was the promise made in the wake of the Gallop inquiry into disability services in the ACT more than 20 years ago.

"It was during this time a commitment was undertaken by the ACT government that all those individual clients living under the care and protection of Disability ACT would continue to receive the necessary care they were provided by the government prior to NDIS, for the rest of their lives," she said.

"Today, sadly, I find it necessary to speak out and expose the lack of adequate support now being provided to some clients who, not of their own choosing, come under the funding umbrella of the NDIS."

A statement from the NDIS said it was "committed to ensuring eligible participants have appropriate accommodation where they feel safe and experience an improved quality of life. This includes choice and control of where and with whom they live".

"The NDIS continues to fund supports associated with two-to-one basis scenarios depending on eligibility," it said.

"Marcus's support coordination funding was increased to further assist him to explore suitable supports and to assist him with his accommodation supports.

"The agency has contacted Sherry to continue to work with her and Marcus's support coordinator on a solution. The agency has also contacted the provider to discuss their obligations and ensure appropriate use of Marcus's funding."

A spokesperson for ACT Minister for Disability Emma Davidson said the government was also looking into Marcus's case.

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"The ACT government remains committed to the principle that individuals who were in ACT government-supported accommodation would have a good transition into the NDIS and throughout their lives and has worked hard with individuals and their families to ensure continuity of services," a statement read.

"In line with this commitment, the ACT government welcomes the Commonwealth and state and territory ministers' agreement for an independent review of the NDIS.

"This review aims to put people with disability back at the centre of the NDIS, restoring trust, confidence and pride in the NDIS amongst them and their families and carers, as well as the broader community."