BACKGROUND: Two polyclinics in Singapore modified systems and trained health professionals to provide person-centred Care and Support Planning (CSP) for people with diabetes within a clinical trial. We aimed to investigate health professionals' perspectives on CSP to inform future developments. METHODS: Qualitative research including 23 semi-structured interviews with 13 health professionals and 3 co-ordinators. Interpretive analysis, including considerations of how different understandings, enactments, experiences and evaluative judgements of CSP clustered across health professionals, and potential causal links between them. RESULTS: Both polyclinic teams introduced CSP and sustained it through COVID-19 disruptions. The first examples health professionals gave of CSP 'going well' all involved patients who came prepared, motivated and able to modify behaviours to improve their biomedical markers, but health professionals also said that they only occasionally saw such patients in practice. Health professionals' accounts of how they conducted CSP conversations varied: some interpretations and reported enactments were less clearly aligned with the developers' person-centred aspirations than others. Health professionals brought different communication skill repertoires to their encounters and responded variably to challenges to CSP that arose from: the linguistic and educational diversity of patients in this polyclinic context; the cultural shift that CSP involved; workload pressures; organisational factors that limited relational and informational continuity of care; and policies promoting biomedical measures as key indicators of healthcare quality. While all participants saw potential in CSP, they differed in the extent to which they recognised relational and experiential benefits of CSP (beyond biomedical benefits), and their recommendations for continuing its use beyond the clinical trial were contingent on several considerations. Our analysis shows how narrower and broader interpretive emphases and initial skill repertoires can interact with situational challenges and respectively constrain or extend health professionals' ability to refine their skills with experiential learning, reduce or enhance the potential benefits of CSP, and erode or strengthen motivation to use CSP. CONCLUSION: Health professionals' interpretations of CSP, along with their communication skills, interact in complex ways with other features of healthcare systems and diverse patient-circumstance scenarios. They warrant careful attention in efforts to implement and evaluate person-centred support for people with long-term conditions.