HM Prison and Probation Service

HMPPS published an algorithmic transparency record (first published 28 April 2025) for the Violence in Prisons Estimator, which it lists as in production with no external supplier. It is an implementation of an Explainable Boosting Machine that estimates "the number of violent incidents that an offender in custody is at risk of being involved in over the next year", using age and measures of the person's assault history and time in custody drawn from Prison NOMIS. The record says it has around 2,000 users each month, mostly prison staff, who use it to identify people who may need extra support and to assess new arrivals, and that its estimates feed the Prison Categorisation tool, which supported around 50,000 categorisation and 83,000 recategorisation decisions between 1 December 2023 and 30 November 2024. It states that "There is always a human decision-maker involved in categorisation decisions" and that the tool should not be the sole source of information in any decision. PublicTechnology reported on 9 July 2025 that the prison service "first began experimenting" with such an algorithm in 2019, and the Ministry of Justice's Justice AI Unit page says the estimator has been available to all prisons since 2019.