| Lead institution | |
|---|---|
| Principal researcher(s) |
Professor Alex Stevens
|
| Police region |
Yorkshire
|
| Collaboration and partnership |
|
| Level of research |
Professional/work based
|
| Project start date |
|
| Date due for completion |
|
Research context
Dame Carol Black’s Independent review of drugs (2020) articulated the scale of the drug problem in England and Wales. There are about three million people who use illicit drugs each year with around 300,000 individuals using heroin and/or crack cocaine. The total annual cost of drug misuse is estimated to be £19.3 billion, including:
- £8.5 billion for drug-related crime
- £6.3 billion for the cost of drug-related death
- £1.4 billion in additional costs of health and social care
Drug-related deaths are also at record levels.
The Black review (2020), the government's 10-year drugs plan (2022), and Sir Brian Leveson’s independent review of the criminal courts (2025) recommended expansion and evaluation of schemes that divert people away from the criminal justice system and into education and treatment. Previous research shows the potential for diversion to increase the proportion of offences that are brought to justice, to cut crime and reduce costs. Less is known about whether schemes have health benefits, have similar or different effects for different types of people, and are cost-effective.
Research questions
The PDD evaluation aims to fill these gaps in knowledge by answering the following research questions:
- what effects have PDD schemes had on offending?
- what effects have PDD schemes had on health outcomes?
- what other effects have PDD schemes had?
- were there inequalities in the use and effects of PDD schemes?
- what were the cost-consequences of PDD schemes for health, police and other service providers?
Funding
The PDD evaluation has received funding from the cabinet office's Evaluation Accelerator Fund.
Research methodology
Work package one – development of intervention manuals and a theory of change
In workshops with stakeholders in three police force areas and nationally, the project we developed detailed descriptions of the schemes that operate in these areas. A theory of change on the alternatives to criminalisation for drug possession was adapted to describe how PDD might bring about outcomes.
Work package two – process evaluation
This package focused on the implementation of PDD and how closely implementation of schemes follows the manuals for the three study forces. The process evaluation also sought to understand how contexts and mechanisms combined to effect change. The research involved semi-structured interviews (n=225) and focus groups (n=6) with police officers, service providers, people who were diverted and people who were not diverted despite being eligible, and analysis of aggregated police data.
Work package three – quantitative outcome assessment
This package assesses the impact of PDD had on offending and health outcomes. It involves complex data linkage across organisations. Analysis will compare outcomes for people who had contact with the police for drug-related offences in forces with PDD schemes, with those for similar people in forces without PDD schemes. Outcomes include reoffending and access to drug or alcohol treatment during the 24-month follow-up. Intention to treat and per protocol analysis is being carried out.
For this analysis, we received data from 44,535 people who were contacted by the police for drug possession or drug-related offences in 15 police forces between October 2021 and September 2022. People who think they may have been included in the data can see the project’s data information sheet.
Work package 4 – cost-consequence analysis
This package looks to establish the financial costs and benefits of PDD, and on which organisations they fall.
Work package 5 – equity assessment
This package will examine whether the use and impact of PDD varies by ethnicity, sex and location.
Work package 6 – realist synthesis
Lastly, this package will bring together all the evaluation findings to detail what works, for who, when and why.
Publications
As of October 2025, the project had produced the following publications.
Hendrie N and others. (2023). The Durham Police Drug Diversion Scheme. Checkpoint: Descriptive Manual. University of Kent
Hendrie N and others. (2023). The Thames Valley Police Drug Diversion Scheme. TVP: Descriptive Manual. University of Kent
Hendrie N and others. (2023). The West Midlands Police Drug Diversion Scheme. DIVERT: Descriptive Manual. University of Kent
Stevens A and others. (2025). Cascading constraint and subsidiary discretion: Perspectives on police discretion from police-led drug diversion and stop and search in England. British Journal of Criminology
Stevens A and others. (2023) Evaluating police drug diversion in England: Protocol for a realist evaluation. Health & Justice
Stevens A and others. (2023). Theory of change of police drug diversion: A revised programme theory. University of Kent
Sutton CE and others. (2025). Triggering motivations for change: Exploring engagement in adult police-led drug diversion programs. Drugs: Education, Prevention and Policy