A girl held in a young offenders’ institution was pinned down and forcibly stripped by a group of male prison guards, according to a watchdog.

Chief Inspector of Prisons Charlie Taylor said he was “deeply shocked” at the findings, which revealed the “incredibly vulnerable” teenage prisoner had been restrained and had her clothes removed by “multiple men” on two occasions at YOI Wetherby in West Yorkshire.

Holding some of the most “challenging” children in the country, the watchdog likened the “complex group” of youngsters behind bars there to the equivalent of being as dangerous as men in category A adult jails.

Nearly half of the children at Wetherby have previously been in council care and the site has the “highest rate of self-harm of any prison in the country”, with officers often having to intervene “multiple times at night” to stop girls trying to harm themselves, inspectors said.

The presence of multiple men pinning her down and removing her clothes will have caused further trauma

Girls were particularly vulnerable to self-harm in Wetherby, with the three held there accounting for more than half the self-harm incidents in the last year – which had been the “key cause of use of force and assaults on staff”, a report published on Tuesday added.

Mr Taylor said: “We were deeply shocked to find adult male officers restraining and stripping an incredibly vulnerable girl not once but twice.

“While they no doubt acted to prevent serious harm, the presence of multiple men pinning her down and removing her clothes will have caused further trauma and, given how predictable the behaviour of this particular girl was, the YOI has no excuse not to have made sure that female officers were in attendance.”

According to justice officials, the officers were responding to a life-threatening situation and acted to prevent the girl from harming herself, with female staff not attending as they had been assaulted earlier in the shift.

But the report told how inspectors had “considerable concerns about the use of all-male teams to cut the clothes of vulnerable girls under restraint”, adding: “This is simply not acceptable.”

Mr Taylor said the incidents occurred despite this being an “entirely predictably pattern of behaviour”.

During the inspection, carried out in November and December last year, wider concerns about how often child inmates were being strip-searched while being restrained and the use of force against them were also raised.

Some 24 children were strip-searched in the last 12 months, with 12 of those taking place while they were being restrained.

Although prison bosses had recorded the decision to carry out a strip-search, “none had recorded the authority to use restraint”, according to the findings.

Techniques that deliberately cause pain in a bid to restrain a child had been used nine times in the last 12 months but were deemed “inappropriate” on each occasion by an independent review panel.

Mr Taylor said it was a credit to the prison’s governor that “most relationships between staff and children were relatively positive compared with other YOIs”, but added: “It was scarcely credible in a jail holding just 165 children with 24 senior managers and 67 other managers that leaders told us they could not give children frequent, structured contact with staff because of a shortage of officers.”

He told BBC Radio 4’s Today programme girls only ended up being housed at Wetherby because of the “closure of failing institutions elsewhere” and that it costs the taxpayer nearly £250,000 a year to hold a child at the YOI.

Children’s Commissioner Dame Rachel de Souza said she was “appalled” by the findings and she had written to Justice Secretary Alex Chalk to ask how conditions are being improved, adding that too many children were being “incarcerated rather than cared for”.

Strip search is an “intrusive and potentially traumatic power” and should “never” be carried out on children by a member of the opposite sex, she said.

These are children who are often vulnerable, traumatised and in many cases have suffered abuse ... The Government must act immediately to improve the lives of these children and to lay out a comprehensive improvement plan across all of these institutions

Andrea Coomber, chief executive of the Howard League for Penal Reform which has opposed the decision to hold girls in Wetherby, said: “It is appalling that the state’s care for vulnerable children could sink to such depths… Some of the findings raise significant safeguarding concerns and potential breaches of human rights.”

Campbell Robb, chief executive of social justice charity Nacro, branded the findings “disturbing” and said the conditions are not how “any child should be treated in a civilised society, whatever they have done in the past”, adding: “The Government must act immediately to improve the lives of these children and to lay out a comprehensive improvement plan across all of these institutions.”

Labour’s shadow justice secretary Shabana Mahmood said the findings were “deeply concerning” and called for an investigation into the treatment of children at Wetherby.

“Under the Conservatives, there is no plan for managing girls in youth custody. They are failing in their duty of care to some of the most vulnerable people in the youth secure estate”, she said.

Mark Fairhurst, national chairman of prison officers’ union the POA, said officers at Wetherby do a “fantastic job” and described the findings as “grossly unfair criticism of staff actions”, adding in a post on X: “These brave staff did the right thing to preserve life – that’s it – end of.”

A Ministry of Justice spokeswoman said: “Custody should always be the last resort for children who commit crime and there has been an almost 70% decrease in the number of girls in youth custody since 2015, averaging just 12 girls in custody last year.

“This small number of girls have exceptionally complex needs and require specialised support, which is why HMYOI Wetherby is providing additional training to staff on self-harm and increasing opportunities for meaningful activity, education and personal development.

“Restraint is only used on children in rare circumstances when there is no alternative to prevent serious harm to the child, other children or staff.”