Abstract Therapist beliefs have been identified as a contributing factor to ‘therapist drift’ in cognitive behavioural therapy (CBT). Scales have been developed to measure therapist beliefs, but none explicitly measure ‘therapy-interfering cognitions’, and there is no research on their usage. The aim of this study was to explore how best to conceptualise such a scale’s content and usage, based on clinicians’ perceptions and experiences of current scales. Three focus groups were conducted, involving 12 participants who were either qualified or trainee CBT therapists. Transcripts were analysed using thematic analysis. Four main themes were generated: (1) The Awareness and Importance of Cognitions, (2) Factors Fuelling Therapist Cognitions, (3) Addressing Therapist Cognitions, and (4) Using the Scale. Participants thought it important to be aware of and address therapist cognitions (not underlying beliefs). Participants emphasised that therapist cognitions are not just products of the individual, but are influenced by external factors. A scale could enable therapists to do better work through reflective practice, as long as it was used not just to identify cognitions but also to support changes in therapist behaviour. A scale could also meet a perceived need for making this part of routine practice. However, participants discussed how therapists might have reservations about disclosing cognitions in this way. Recommendations for current practice, and future research developing such a scale, are made. Key learning aims (1) To describe the phenomenon of therapist drift, and the contributions of therapist beliefs to this. (2) To explore the usage of current scales for measuring therapist beliefs. (3) To understand, based on therapist experience, how to address therapist beliefs in current practice using scales.