People with disabilities in the criminal justice system feel like they exist in a "black hole" after an international torture prevention body cancelled a visit to Australia. 

Human rights advocates have raised concerns following the United Nations (UN) Subcommittee on the Prevention of Torture's (SPT) termination of its planned trip to inspect places of detention including jails, juvenile centres and secure disability and mental health facilities.

It followed the decision by the SPT last October to suspend a 12-day visit to Australia, mid-way through the trip, after inspectors were denied access to several detention facilities.

Last month, the UN said the visit had now been cancelled because the New South Wales and Queensland governments would not provide "unrestricted access" to their detention settings.

Dana Levitt of Sydney firm Levitt Robinson, who specialises in human rights law, said Australia had failed to meet its international obligations and disabled detainees, including many young Indigenous people, were in a "spiral of hopelessness".

"They don't have any visibility and they can't really effectively advocate or generate awareness of their plight," she said.

"We're locking them up and throwing away the key … their behaviour is misinterpreted as wilful defiance or criminal intention but it's often just the product of their disability."

Last year, the disability royal commission heard evidence about the over-representation of people with disability in the criminal justice system and the lack of data collection.

Ms Levitt said the experience of juveniles in facilities like Western Australia's Banksia Hill Detention Centre, where research released in 2018 found nine out of 10 detainees lived with disability, needed the attention of international inspectors.

Ms Levitt is working on a class action being brought against the Western Australian government by current and former detainees of Banksia Hill.

More than 700 people, most of them Indigenous and many with disabilities, have joined the action.

Ms Levitt said a UN visit was important because it would allow international inspectors to better scrutinise Australia's facilities.

"People in detention who are disabled feel hopeless in that they recognise they are sort of in a black hole," she said.

In 2017, Australia ratified the UN Optional Protocol to the Convention Against Torture (OPCAT), which agrees to oversight for places of detention through external bodies like the SPT.

Aside from Australia, the only other country to have an inspection visit cancelled by the UN body is Rwanda.

Less scrutiny on 'egregious human rights abuses'

Patrick McGee, the national coordinator for Australians for Disability Justice, said the terminated UN visit had left detainees across the country feeling "voiceless" and removed pressure on Australia to account for itself.

"People with disability and mental health disorders are detained in places where there are egregious human rights abuses such as arbitrary detention and cruel and degrading treatment," Mr McGee said. 

"In Australia, there is almost no external formal monitoring of places of detention and agencies that are responsible are hugely underfunded to do the job they are required to do and lack the legislative teeth to implement changes."

Mr McGee is the co-guardian of a First Nations man who has been detained for 16 years and remains in the Forensic Disability Unit in Alice Springs, with no date for release.

The man, known by the pseudonym Winmartie, lives with epilepsy and cognitive disability and was convicted of manslaughter by reason of diminished responsibility over the death of his uncle in 2007.

Mr McGee said the cancellation of the SPT visit was a missed opportunity for people like Winmartie.

'Wake up to yourselves'

Mr McGee and other advocates will meet in July at a forum on the treatment of people in places of detention to discuss a national plan of action.

One of those attending will be UNSW PhD researcher Karen Daniels, whose work examining the number of people who have died in or been subject to forensic detention was presented to the UN's Committee Against Torture last year.

Forensic hospitals are highly secure mental health facilities for people who have been deemed not criminally responsible by the justice system because of mental illness and/or cognitive impairment. 

Ms Daniels said the cancelled SPT visit would limit the opportunities for patients to have their voices heard by a completely independent group of people.

"Forensic patients have important stories to tell and some patients only trust external voices," Ms Daniels said.

"Some patients have experienced extended time in seclusion or the overuse of chemical and mechanical restraints, so it is important that patients have access to independent advocates who will safeguard their human rights."