BACKGROUND: Combined physical and psychological programmes (CPPP) are recommended for people with disabling low back pain (LBP). Cognitive Functional Therapy (CFT) is a physiotherapist-led low intensity CPPP with positive effects in previous studies. The clinical and cost effectiveness of CFT has not previously been evaluated in a randomised controlled trial (RCT) in the United Kingdom (UK) National Health Service (NHS). Before a definitive RCT can be completed it is necessary to determine if completing such a study is possible. PURPOSE: To determine the feasibility of completing a definitive RCT, that will evaluate the clinical and cost-effectiveness of CFT in comparison to usual physiotherapy care for people with persistent LBP in the UK NHS. METHODS: A pragmatic two-arm parallel feasibility RCT comparing CFT with usual physiotherapy care for people with persistent LBP will be completed. Sixty participants will be randomly allocated to receive CFT or usual physiotherapy care. The primary outcome will be feasibility of completing a definitive RCT. Participant reported outcome measures will be recorded at baseline, three, six and twelve-month follow-up, including disability, pain intensity, quality of life and psychosocial function. Data will be analysed descriptively. A qualitative process evaluation will explore the acceptability of the research processes and interventions. DISCUSSION: The rationale and methodological design of a mixed methods feasibility RCT is presented. This study aims to inform the planning, design and completion of a future definitive RCT in the UK NHS. The results will be disseminated through peer reviewed open access journal publication.