Most children in young offender institutions (YOIs) spend “most of their time locked alone in their cells”, according to an inspection report.

The report laid bare the “failure” by the Youth Custody Service to “create environments in which staff and children are able to form positive, appropriate relationships”.

The findings were based on interviews with children aged 10 to 18, as well as staff, at YOIs in Bridgend in South Wales, Stoke-on-Trent, and the Wetherby and Keppel units in West Yorkshire.

A Ministry of Justice spokesperson said it was “improving the support available to those in the youth estate and strengthening their relationships with staff”.

Authored by Chief Inspector of Prisons Charlie Taylor, the report found there was “little that was reliable or consistent about life in [many] YOIs”.

Campbell Robb, chief executive at social justice charity Nacro, said the report was “more evidence that the environment in our YOIs is profoundly harmful for children, many of whom are already extremely vulnerable”.

The report found fewer than half of the children in custody felt cared for by staff, while one in three said there was no member of staff they could turn to if they had a problem.

“This is concerning because staff rely on meaningful, trusting relationships to encourage children to engage with education, health care or offending behaviour programmes, as well as to defuse conflict and violence,” it said.

According to the report, “there is mounting evidence that relationships between staff and children in custody are a key element in delivering better outcomes”.

However, children being locked up for most of the day meant “there was very little time for staff to get to know those in their care”.

As of March, there were 502 young people detained at YOIs in England and Wales.

“We don’t have the power to change a lot and the kids know it,” said one YOI staff member.

At Wetherby YOI, children told inspectors it could take up to 45 minutes to get a response after ringing their cell bell, while most wings did not provide opportunities for exercise, association or time for domestic tasks during the week.

At Werrington near Stoke, one child said they had pressed their cell bell five times to get a plastic cup.

Staff also said there was “simply no time” to make a positive impact on children’s lives.

Mr Robb, whose organisation supports people in the criminal justice system, said the report “should prompt the government to take urgent action”.

“We urge them to ensure that children should only be held in custody as an absolute last resort and to ensure a safe, rehabilitative environment in all YOIs to give young people the best possible chance to change.”

The Ministry of Justice said its priority “remains supporting [children’s] long-term rehabilitation to cut crime, which is why we’re improving the support available to those in the youth estate and strengthening their relationships with staff.”

A spokesperson added: “Custody remains a last resort for children, used only in the most serious cases.”