ObjectivesTo determine the feasibility of completing a definitive randomised controlled trial (RCT), evaluating the clinical and cost-effectiveness of Cognitive Functional Therapy (CFT) in comparison to usual physiotherapy care (UPC), for people with persistent low back pain (LBP). Design and settingA two-arm parallel feasibility RCT completed in a United Kingdom (UK) Secondary Care National Health Service (NHS) physiotherapy service. ParticipantsSixty adult participants who reported LBP lasting for more than three months, that was not attributable to a serious (e.g. cancer) or specific (e.g. radiculopathy) underlying cause, were invited to participate. Participants were allocated at random to receive CFT or UPC. InterventionsCognitive Functional Therapy and Usual Physiotherapy Care for persistent LBP. Main outcome measuresThe primary outcome was the feasibility of completing a definitive RCT, defined by recruitment of at least 5 participants per month, delivery of CFT per protocol and securing relevant and acceptable outcome measures. Data concerning study processes, resources, management and participant reported outcome measures were collected at baseline, 3, 6 and 12-month follow-up. ResultsSixty participants (n = 30 CFT and n = 30 UPC) were recruited with 80% (n = 48), 72% (n = 43) and 53% (n = 32) retained at 3, 6 and 12-month follow-up respectively. NHS physiotherapists were trained to competence and delivered CFT with fidelity. CFT was tolerated by participants with no adverse events. Relevant and clinically important outcome data were collected at all time points (0.4%, 3%, 1% and 0.8% of data was missing from the returned outcome measure booklets at baseline and 3, 6 and 12-month follow-up respectively). The Roland-Morris disability questionnaire was considered the most suitable primary outcome measure with a proposed sample size of 540 participants for a definitive cluster RCT. ConclusionIt is feasible to conduct a randomised study of CFT in comparison to UPC for NHS patients. A future study should incorporate an internal pilot to address aspects of feasibility further, including participant retention strategies. Clinical trial registration numberISRCTN12965286 Contribution of the paper•Cognitive Functional Therapy (CFT) has shown encouraging results for reducing pain and disability in people with persistent LBP in previous clinical trials. The clinical and cost-effectiveness of CFT has not previously been evaluated in a definitive trial in the United Kingdom National Health Service. This is the first study to evaluate the feasibility of completing such a trial.•The findings of this study confirmed that;•NHS patients can be recruited on time and to target, with no safety concerns regarding a randomised controlled trial.•NHS physiotherapists can be trained to competence to deliver CFT with fidelity.•Clinically relevant and important data can be collected using standardised outcome measures.•New knowledge about the feasibility of completing a definitive trial of CFT in the UK NHS has been gained.