An investigation has detailed “horrific and systemic” historical abuse of people with learning disabilities in state care facilities in New Zealand.

Between 1950 and the 1980s, 100,000 New Zealand children and vulnerable adults were taken into state care, and earlier reports have revealed the abuse of more than 1,000 children in state care homes, and of mental health patients in psychiatric facilities.

A new study for the Human Rights Commission focuses on accounts of the state’s treatment of people with learning disabilities.

The commission has repeatedly called on the New Zealand government to follow the lead of the UK and Australia in conducting an independent inquiry into abuse in state institutions, but the government has so far refused.

The government institutionalised disabled people at three times the rate of equivalent countries, the report states, with many subjected to beatings, sexual assaults, isolation and long periods of restraint.

The disability rights commissioner, Paul Gibson, told the Guardian there were also numerous anecdotal accounts of wards of the state between the 1940s and 70s being subjected to forced lobotomies, sterilisations and having drugs such as LSD tested on them.

Gibson said some children with learning difficulties were forcibly removed from their families by police and social workers who put them into often violent and neglectful state care.

“In New Zealand it started off with the eugenics movement – who was fit to be a citizen. It was part of the pervasive hegemony of what a good citizen looked like – and that was deemed to be the British colonial, non-disabled model,” he said.

Among the cases cited by the study is that of Robert Martin, a ward of the Kimberley Centre in Levin until he was 15 and now an activist who sits on the United Nations Committee on the Rights of Persons with Disabilities, who described his years in state homes in his biography, Becoming a Person.

“Me and my friends were denied our basic human rights such as freedom, opportunities to learn and to have ordinary experiences,” wrote Martin, who said he was subjected to physical, emotional and sexual abuse during his years in care. “The only way to express ourselves was by behaving in a way the staff called ‘challenging’. For some of us this meant engaging in self-injurious activities – biting arms and hands, banging heads.”

Other accounts spoke of being sexually assaulted by carers, tied up to beds, locked in seclusion rooms, defecating without privacy and being starved of care and attention, sometimes for decades.

“In hospitals you get abused: you get hit, and they make you a slave,” said Mavis May, who was in and out of state institutions for 30 years. “The hardest thing for me was closed doors, locked doors … We had a special room for when we were naughty. They called that room the naughty room. They shut us up. The door had three locks: one at the top, one in the centre and one at the bottom. We had to stay there all night.”

Gibson said that although the most brutal mistreatment had waned, there were still reports of autistic children being locked up in dark cupboards at school or held in seclusion for long periods.

“We still do extreme medical intervention and experimentation on intellectually disabled people today, which we wouldn’t do to anyone else,” he said. “We know in the last eight months there has been the uncovering of six-year-old kids with autism who have been put in cupboard-sized dark rooms at school. We are aware of others put in seclusion who have drunk their own urine out of desperation. This is what happens to people when they are out of sight, out of mind, so we have to remain vigilant so this never happens again.”

The Labour party, the Greens and the Maori party have all committed to holding an inquiry if they win power in an upcoming election. Nearly half of children in state homes in the 1970s were Maori.

The Greens co-leader Metiria Turei said: “It seems everyone but the government realises that an inquiry is essential to help the victims find some sense of closure and to ensure that tamariki Maori in state care now and in the future are protected from abuse.”

Social welfare bodies such as Unicef and the Maori Women’s Welfare League also support the calls for an independent state inquiry.

Gibson said: “I think the government’s response to date has been mean-spirited. This stuff did not generally happen under this government watch, but this government has the opportunity to set things right now.”