Children in immigration detention are being used as “bargaining chips” by the immigration minister in order to win passage for his temporary protection visa legislation, Australia’s human rights commissioner has said.

“We find it deeply offensive that children are being used as leverage, because … we are destroying children’s lives in these places,” Gillian Triggs told Guardian Australia.

Triggs, whose draft report of the commission’s inquiry into children in immigration detention has been sent to the Department of Immigration and Border Protection, said Scott Morrison had an “ideological obsession” with granting temporary protection and was refusing to process refugee claims because, legally, he could only grant permanent visas at the moment.

Last year Morrison attempted to introduce temporary protection visas (TPVs) via regulation before it was disallowed by the Senate.

But legislation currently before the Senate would reintroduce TPVs, as well as removing Australia’s international protection obligations under the refugee convention from domestic law.

“The minister is using the children in detention, along with the Palmer United party, as bargaining chips to get what he wants, which is temporary protection visas. We find this deeply offensive to international law, to the rights of the child, that they are being held as a means to ensure the minister gets what he wants – temporary visas.”

Previously, the human rights commission has opposed TPVs but, Triggs said, she would accept them “with some reluctance” if it meant children were released from detention.

The average length of detention for a child in the Australian immigration system was between 14 and 15 months.

“How long can we stand on legal principle if the children are suffering? And they are seriously suffering. I think we’ve reached a position in which we feel it’s a practical matter, if the children can be released, even on a temporary visa, we’ll fight the next battle another day.”

Speaking at the Andrew & Renata Kaldor Centre for International Refugee Law annual conference at the University of NSW on Monday, Triggs discussed her inquiry report, the Forgotten Children, a draft of which was handed to government last month. It has not been made public yet.

On detention centre visits, Triggs said she found “unspeakably bad” conditions.

Medical experts reported to the inquiry that many children were arriving in Australia’s care traumatised from experiences in their home countries, and their conditions were worsening in detention.

“The fact of their detention and the traumatic circumstances of their parents exacerbates the situation. They will suffer for many, many years once they are released.”

Triggs said the public would find the report confronting, particularly photographs showing the use of force against children by security agents, as well as the individual stories of asylum seekers.

“There was a lovely young woman, a model and an architecture student in Afghanistan, who threw herself off the top of a building and had huge scars over her legs and arm and neck from a very genuine suicide attempt. These things were covered up by the department. So it was imperative for us to go there independently to see what the facts were.”

During the minister’s appearance before the inquiry hearings in August, Triggs and Morrison clashed heatedly over whether the conditions in detention centres were “prison-like”.

“The truth is the conditions the children and their families are being held in is far worse than any prison,” Triggs said Monday.

“There’s the lawyers’ point they have not been charged with any offence and they’ve never had their day in court, ever. They have no idea when they’re going to be getting out, little to no access to their lawyers and they can’t be visited by friends or family.

“The other less obvious point, because no one can see it, is that families are held in three-metre by two-metre reconstituted shipping containers, where they are living cheek by jowl and disease spreads. Medical experts say virtually every child on Christmas Island is sick. Mothers can’t put their babies down on the ground because it’s stone and phosphate gravel: this is far worse than any prison we could possibly operate.”

Morrison’s office has been approached for comment.