BackgroundThe National Institute for Health and Care Excellence (NICE) recommends that cognitive behaviour therapy (CBT) is offered to all patients with a psychosis diagnosis. However, only a minority of psychosis patients in England and Wales are offered CBT. This is attributable, in part, to the resource-intensive nature of CBT. One response to this problem has been the development of CBT in brief formats that are targeted at a single symptom and are deliverable by briefly trained therapists. We have developed Guided self-help CBT (the GiVE intervention) as a brief form of CBT for distressing voices and reported evidence for the feasibility of a randomised controlled trial (RCT) when the intervention was delivered by briefly trained therapists (assistant psychologists). This study will investigate the clinical and cost-effectiveness of the GiVE intervention when delivered by assistant psychologists following a brief training.MethodsThis study is a pragmatic, two-arm, parallel group, superiority RCT comparing the GiVE intervention (delivered by assistant psychologists) and treatment as usual to treatment as usual alone, recruiting across three sites, using 1:1 allocation and blind post-treatment and follow-up assessments. A nested qualitative study will develop a model for implementation.DiscussionIf the GiVE intervention is found to be effective when delivered by assistant psychologists, this intervention could significantly contribute to increasing access to evidence-based psychological interventions for psychosis patients. Furthermore, implementation across secondary care services within the UK’s National Health Service may pave the way for other symptom-specific and less resource-intensive CBT-informed interventions for psychosis patients to be developed and evaluated.Trial registrationCurrent Controlled Trials ISRCTN registration number: 12748453. Registered on 28 September 2022.