The purpose of the present study was to investigate factors influencing the implementation of a model for service delivery and organisation in mental healthcare. A qualitative case-study approach was employed involving in-depth interviews with 25 service providers from across mental health and social care in one local authority area in northern England. Purposive sampling achieved a broad coverage across geographical areas, voluntary and statutory services, and primary, secondary and specialist mental healthcare. The findings indicate that implementation was influenced by three interrelated factors: the means by which the model was introduced to the workforce; use of the model itself by service providers; and the broader service context. Thus, negative reactions to the way the model was initially presented strongly influenced service providers' subsequent views of it. Moreover, observations regarding the broader context of mental healthcare revealed a service that was ill-equipped to manage change because of over-stretched resources and that was disinclined to accept imposed change because of poor staff morale. Finally, differential interpretation of the model's tiers by service providers led to defensive practice that manifested itself as over-referral of service users within the system. Changing practice behaviour is a complex process, particularly at a service level that consists of numerous professional groups with differing cultural norms. Successful reorganisation of services is unlikely if those responsible for delivering care are not part of the process of change. Moreover, unsuccessful attempts to change professional practice may exacerbate existing tensions within a workforce, which may be to the detriment of those requiring care. A full diagnostic analysis of the system, including service providers' concerns, should be carried out before introducing change or reconfiguring services.