Evaluating a Workbook to Promote Autistic Wellbeing

The goal of this clinical trial is to examine the feasibility and acceptability of a brief guided self-help wellbeing intervention for autistic adults accessing UK secondary mental health services. The study also aims to begin to evaluate whether use of the workbook is associated with any changes in wellbeing. The main questions it aims to answer are: 1. Is it feasible to recruit and retain autistic adults to participate in the study? 2. Do participants find the workbook acceptable and relevant? 3. Are there measurable improvements in wellbeing following workbook use? 4. What changes, if any, do participants recommend for future versions of the intervention? Participants will: * Take part in 4-6 sessions of 30-60 minutes using the guided self-help workbook with the support of a trained National Health Service support worker, assistant psychologist, or mental health professional * Complete wellbeing questionnaires before, during, and after using the workbook * Complete brief daily wellbeing ratings throughout the study * Take part in a 1:1 semi-structured interview of up to an hour to discuss their experience of the workbook

Inclusion Criteria: * A pre-existing diagnosis of autism OR on a waiting list for autism assessment OR self-identified as autistic and scoring above cut-off on the autism quotient (AQ-50) screening questionnaire. * Aged 18 years or over and able to give informed consent to participate. * Under the care of a community-based mental health team in Kent and Medway Mental Health NHS Trust and not due for discharge during the study period. * Have already completed assessment processes (including risk assessment) during intake by the clinical team and a management plan is in place. * The named clinician assesses that the individual is in sufficiently stable condition to participate in the study, and is likely to remain engaged in the intervention. * Proficiency in reading and writing English. * If on medication for mental health, the dose is stable (minimum of 3 months) with no planned changes during the study. Exclusion Criteria: * Presence of a moderate to severe learning disability that would limit independent engagement with self-help materials. * Engaged in another psychological therapy or psychologically-informed intervention, or due to begin another during the study. * Current acute mental health crisis or elevated risk to self/others requiring intensive intervention (assessed via clinical team judgement). * Insufficient capacity to engage with the study protocol or complete measures (as determined by the care team).