NDIS architect says scheme not working as intended

"It's inevitable when you introduce a scheme of this magnitude, which is so transformational, which is world leading and a scheme which Australians are justifiably proud of, that it does not work," he told ABC Radio on Friday.

"Not every aspect of it works as intended."

Professor Bonyhady said the NDIS had become an all or nothing approach for those with disability to receive support.

"You're either inside the NDIS getting its benefits or out," he said.

"Because there's virtually no supports outside the scheme, people are beating a path toward the door.

"The absence of support outside of the scheme is not only deeply unfair, it also leaves them over time with increased disabilities, increased age, which then makes them eligible for the scheme and so it's the exact opposite to what our insurance scheme is meant to do."

The NDIS is on track to become the single highest cost to the federal budget, eclipsing Medicare.

By 2025/26, the NDIS is expected to cost more than $50 billion.

NDIS Minister Bill Shorten has pledged to reform the scheme, with the interim report into the review to be handed down soon.

The government pledged to rein in spending growth of the scheme to eight per cent by July 2026.

Prof Bonyhady said other disability services needed to take a bigger role.

"The NDIS cannot be an oasis in the desert and it neither can be an island where every other system expects it to do the heavy lifting," he said.

"People are forced to present their worst side in order to enter the scheme and then receive a package of support to support their needs."

The NDIS architect said the growth targets implemented in the past federal budget did not represent a cut to the scheme.

"The measures that are in the budget should be looked at as a down payment on building the capacity of the agency to deliver a fair and sustainable scheme," he said.

"It's quite clear that this scheme needs to be affordable, its costs need to be predictable, because in the absence of that, there is a risk of the erosion of public trust and confidence and government trust and confidence in the scheme."