Project Guardian: redesigning the custody journey to reduce child reoffending

Randomised Control Trial Status


Trial Hypothesis

​Whether a ‘Guardian Briefing’ can reduce the likelihood of a child taken into custody being rearrested.

Geographical area


Research Institution / Organisation

College of Policing

In Collaboration With

Metropolitan Police Service

Project Start Date

August 2020

Participants - inclusion criteria

​All children arrested in three custody suites during the trial period will be considered for involvement for in the trial.
The exclusion criteria will be as follows:

  • The appropriate adult (AA) must be a family member (not an AA scheme member or volunteer)

  • The appropriate adult must speak English (as evaluated by the custody staff not requiring an interpreter


The trial will be run as police custody “business as usual”. Participants will be given the option of opting out of the post-custody communication, and will not be forced to engage in the survey.


Target Sample Size

Based on custody traffic in previous years, it is anticipated that around 1000 children will be considered for randomisation in the initial 3 month period.

Study Design

A two arm, individually randomised controlled trial. Each child arriving at custody will be randomly assigned (via a website) to the treatment or control group.


​The intervention will be separated into two parts: one while the child is in custody, and follow-up messaging after they leave. When the child is arrested, selected parents will be taken aside, and shown a short video about signs of gang involvement. They will then have a discussion with a local detention offer about support in their local area, and complete a survey assessing their current trust in policing. A pre-defined period after they leave custody (a week and a month), the parent will receive follow-up messaging in the form of text and email messages reminding them of the commitments they made, the support agencies they highlighted as particularly helpful.

Outcome Measures

​The primary outcome for this trial will be whether a child re-offends in the period after being treated. The secondary outcome will be a measure of confidence and trust in the policing system by the appropriate adult, as measured by the in-custody survey.

Date last updated

Thursday 06 May 2021
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