The Government Says

Research: Expanded drug rehabilitation requirement drug testing: Process evaluation

Research: Expanded drug rehabilitation requirement drug testing: Process evaluation
Local copy of expanded-drug-rehabilitation-requirement-drug-testing-process-evaluation-report.pdf

https://www.gov.uk/government/publications/expanded-drug-rehabilitation-requirement-drug-testing-process-evaluation

seen at 10:08, 18 June in Ministry of Justice - Activity on GOV.UK.