In the United Kingdom (UK), ethical guidance for doctors assumes a therapeutic setting and a normal doctor-patient relationship. However, doctors with dual obligations may not always operate on the basis of these assumptions in all aspects of their role. In this paper, the situation of UK occupational physicians is described, and a set of models to characterise their different practices is proposed. The interaction between doctor and worker in each of these models is compared with the normal doctor-patient relationship, focusing on the different levels of trust required, the possible power imbalance and the fiduciary obligations that apply. This approach highlights discrepancies between what the UK General Medical Council guidance requires and what is required of a doctor in certain roles or functions. It is suggested that using this modelling approach could also help in clarifying the sources of moral conflict for other doctors with "dual obligations" in their various roles.