Plot: BBC Panorama goes undercover to expose harrowing evidence of children and young people being hurt and threatened by custody officers who are supposed to protect them. Secret filming at a privately run youth prison, paid more than £10m in 2015 by the government to provide high-quality education and to rehabilitate some of the most vulnerable youngsters in the prison system, reveals some officers mistreating their charges and many more tolerating the behaviour or even helping to cover it up