Every death in police custody is a tragedy and this is a priority area for the Government. The Ministerial Council on Deaths in Custody is currently undertaking a programme of work to find solutions to complex issues as highlighted in Dame Elish Angiolini’s Independent Review on Deaths and Serious Incidents in Police Custody. The Ministerial co-chairs will report on progress in Autumn 2018.
Official statistics of deaths in police custody are published annually by the Independent Office for Police Conduct (IOPC). Available here: https://www.policeconduct.gov.uk/research-and-learning/statistics/annual-deaths-during-or-following-police-contact-statistics
The number of deaths in immigration removal centres while held under immigration powers (IRCs) is a subset of published detention data (table dt_6) in the Home Office quarterly Immigration Statistics release. They are not released as part of immigration statistics. The latest data, published in ‘Immigration Statistics, October to December 2017’, is available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/681703/detention-oct-dec-2017-tables.ods