The Government Says

Guidance: Interception, monitoring and security of prisoner communications policy framework

Guidance: Interception, monitoring and security of prisoner communications policy framework
Local copy of interception-monitoring-pf.pdf
Local copy of interception-pf-annex-a-e.zip

https://www.gov.uk/government/publications/interception-monitoring-and-security-of-prisoner-communications-policy-framework

seen at 10:44, 11 August in Ministry of Justice - Activity on GOV.UK.