The objective of this study was to investigate the judgements of British doctors, nurses and midwives about behaviour which complies with a protocol, violates a protocol, or constitutes an improvisation where no protocol exists. Primary data were collected on the judgments of hospital healthcare professionals (N = 310) from three specialties in each of three hospitals. Respondents were required to judge the appropriateness of the behaviour of a fellow professional in each of nine hypothetical scenarios generated on the basis of previous focus group discussions. They were also asked how likely they would be to report this professional to a senior member of staff. Within the scenarios, both behaviour with respect to the relevant clinical protocol and outcome for the patient were experimentally manipulated. Data were collected using a survey questionnaire. The three professional groups studied (doctors, nurses and midwives) were found to make significantly different judgements. Crucially, doctors judged the violation of a protocol as less inappropriate than did nurses or midwives. Midwives were disapproving of violations, even when the patient outcome was good. These differences were reflected in the ratings of reporting likelihood. The proliferation of clinical protocols likely to occur in Britain in the coming years will need to be managed with great care if the regulation of clinical behaviour is the goal. Particular care will be needed to avoid the exacerbation of professional tensions.