The Government takes proscription offences seriously. Investigations into the activities of proscribed organisations or individuals who may be members or supporters of proscribed organisations are an operational matter for the police and intelligence agencies. It would not be appropriate to publish data on intelligence related matters.
The Government publishes quarterly national statistics on the use of police powers under the Terrorism Act 2000 and subsequent relevant legislation in Great Britain. This includes information on arrests, charges and convictions for proscription offences. The most recent publication up to year ending March 2020, was published on 11 June on GOV.UK: https://www.gov.uk/government/statistics/operation-of-police-powers-under-the-terrorism-act-2000-financial-year-ending-march-2020.
The quarterly publications establish transparency by ensuring that data is publicly available on the use of police powers in a consistently categorised way. As with all crime statistics published by the Home Office, the data published in the Terrorism statistics are offence based, where police provide a count of the number of offences recorded. Data providers are not required to provide further detail on events leading to the arrest, as to do so would place a disproportionate burden on the organisations responsible. This includes the National Counter-Terrorism Police Operations Centre, the Crown Prosecution Service’s Counter-Terrorism Division, the Metropolitan Police Service and the National Counter-Terrorism Policing Headquarters. As with all Official Statistics, we continually review outputs taking account of user needs.