The number of juveniles subjected to controversial isolation measures in Victoria’s beleaguered youth justice system surged in the year after the Andrews government came to power, striking new figures reveal.

The previously unpublished data, obtained by The New Daily under Freedom of Information laws, shows that 237 youths aged 10 to 17 were held in isolation in 2015 – Premier Daniel Andrews’ first full year in office – up 40 per cent from the 170 in the previous 12 months.

The practice, where a detainee is separated from other inmates and locked in a secure room, is banned as punishment for minors under Victorian law, but may be used where people or property are under threat and all other steps have failed.

Human rights groups have criticised the use of isolation on children for its detrimental effect on their development and mental health.

But a spokesperson for the Department of Health and Human Services described the use of isolation cells as an “important tool” in the youth justice system.

“Isolation, separation and lockdown are important tools used to safely manage youth justice facilities and to maintain order,” the spokesperson said.

“The use of isolation is set out by legislation. Since early last year, new procedures require the approval of senior management.”

System in crisis

The disclosure of a surge in harsher control measures comes as Commissioner for Children and Young People Liana Buchanan conducts an investigation into the use of isolation, lockdowns and separation inside Victoria’s youth justice regime, following reports last year of a teen being placed in isolation for 10 days.

The figures provided to The New Daily do not indicate the time spent in isolation or the justification in each case.

The revelations also follow the Labor state government’s announcement on Monday of plans to build a $288 million youth prison in Melbourne’s south-west, after the release of a scathing review of conditions at existing facilities by the Victorian Ombudsman.

In a report tabled before the state parliament on Monday, Ombudsman Deborah Glass raised concerns about the excessive use of lockdowns – where all juveniles in a unit are locked in their rooms whether or not they are involved in a disturbance – as well as staff shortages, and the denial of adequate bedding and toilet facilities.

Ms Buchanan said the data obtained by The New Daily was “concerning” and there was a significant likelihood it actually underestimated the use of isolation in the youth justice system.

“That’s based on very detailed work that we’ve been doing in the context of our inquiry and a lot of gaps or issues we’ve identified with record keeping,” she said.

Ms Buchanan, whose detailed findings are subject to parliamentary privilege until next month, said she’d seen evidence of isolation being imposed for extended periods of time, despite the narrow parameters for its use outlined in legislation.

Hugh de Kretser, executive director of the Human Rights Law Centre, said greater use of isolation was likely to exacerbate rather than quell unrest in the youth detention regime.

“The data backs up what we’ve been observing – that there’s been increasing numbers of children being locked in their cells for up to 23 hours a day. This is due to a mix of staff shortages and the overuse of isolation plans,” Mr de Kretser said.

Victoria’s youth justice system has come under harsh scrutiny in recent months following repeated disturbances at the state’s two dedicated detention facilities in Parkville and Malmsbury, and an uptick in young offenders carrying out serious crimes such as carjackings and home invasions.

Rioting at the Parkville centre last month left the facility unusable, prompting the government to move juveniles to a specially adapted unit at Barwon Prison, which is designed for adult criminals.

Just a fortnight ago, 15 offenders broke out of the Malmsbury detention centre, embarking on a 24-hour crime spree that included assaults, home invasions and armed robberies.

The Liberal Party opposition seized on the isolation numbers as evidence that the Premier and Families and Children Minister Jenny Mikakos were unable to manage the youth justice system.

“The warning signs that Daniel Andrews and Minister Jenny Mikakos had lost control of our youth justice system were obvious from the start,” said Georgie Crozier, the shadow minister for families and children.

“It’s clear now the Andrews Labor government have no excuses, their mismanagement of the system is clear and the blame lies with them.”