BACKGROUND: UK cancer mortality is worse than in many other high-income countries, partly because of diagnostic delays in primary care.

AIM: To understand beliefs and behaviours of GPs, and systems of general practice teams, to inform the Think Cancer! intervention development.

DESIGN AND SETTING: An embedded qualitative study guided by behaviour change models (COM-B [Capability, Opportunity, Motivation - Behaviour] and theoretical domains framework [TDF]) in primary care in Wales, UK.

METHOD: Twenty qualitative, semi-structured telephone interviews with GPs were undertaken and four face-to-face focus groups held with practice teams. Framework analysis was used and results were mapped to multiple, overlapping components of COM-B and TDF.

RESULTS: Three themes illustrate complex, multilevel referral considerations facing GPs and practice teams; external influences and constraints; and the role of practice systems and culture. Tensions emerged between individual considerations of GPs (Capability and Motivation) and context-dependent external pressures (Opportunity). Detecting cancer was guided not only by external requirements, but also by motivational factors GPs described as part of their cancer diagnostics process. External influences on the diagnosis process often resulted from the primary-secondary care interface and social pressures. GPs adapted their behaviour to deal with this disconnect. Positive practice culture and supportive practice-based systems ameliorated these tensions and complexity.

CONCLUSION: By exploring individual GP behaviours together with practice systems and culture we contribute new understanding about how cancer diagnosis operates in primary care and how delays can be improved. We highlight commonly overlooked dynamics and tensions that are experienced by GPs as a tension between individual decision making (Capability and Motivation) and external considerations, such as pressures in secondary care (Opportunity).