The concept of Service Model Fidelity is considered as a parallel process to Treatment Fidelity in evidence-based psychological therapies. NHS Talking Therapies (formerly IAPT) aimed to increase access to an expanded, upskilled workforce on a national scale. This included systematic training, supervision and front-line service delivery, emphasising treatment fidelity to evidence-based interventions. A further feature of NHS Talking Therapies was modernising and restructuring of the health system that housed these trained practitioners. The term ‘service model fidelity’ (Cromarty, 2016) was coined to emphasise service modernisation aspects as a distinct entity. A definition of the latter is included. Examples of service model fidelity and of service model drift, are outlined to distinguish these from therapist drift. This links to past literature recommending changes in traditional mental health service design and emergent evidence from NHS Talking Therapies. The latter examines publicly available data identifying characteristics of service design, which appear to be predictors of enhanced clinical outcome. Challenges in modernising health systems are discussed and conclusions are made highlighting the crucial role of service model when delivering evidence-based therapies. Suggestions for further research into service configuration to improve experiences of service users are considered. This includes ongoing exploration of service design being more than a qualitative feature, and increasingly appearing as a key factor in enhanced clinical outcome.

1. (1) To identify service model fidelity as separate entity to treatment fidelity.

2. (2) To provide a clear definition of service model fidelity.

3. (3) To delineate therapist drift from service drift.

4. (4) To further examine the role of service model in delivering evidence-based interventions.