Introduction Whiplash-associated disorder (WAD) causes substantial social and economic burden internationally. Up to 60% of patients with WAD progress to chronicity. Research therefore needs to focus on effective management in the acute stage to prevent the development of chronicity. Approximately 93% of patients are classified as WADII (neck complaint and musculoskeletal sign(s)), and in the UK, most are managed in the private sector. In our recent systematic review, a combination of active and behavioural physiotherapy was identified as potentially effective in the acute stage. An Active Behavioural Physiotherapy Intervention (ABPI) was developed through combining empirical (modified Delphi study) and theoretical (social cognitive theory focusing on self-efficacy) evidence. This pilot and feasibility trial has been designed to inform the design of an adequately powered definitive randomised controlled trial.

Methods and analysis Two parallel phases. (1) An external pilot and feasibility cluster randomised double-blind (assessor and participants), parallel two-arm (ABPI vs standard physiotherapy) clinical trial to evaluate procedures and feasibility. Six UK private physiotherapy clinics will be recruited and cluster randomised by a computer-generated randomisation sequence. Sixty participants (30 each arm) will be assessed at recruitment (baseline) and at 3 months postbaseline. The planned primary outcome measure is the neck disability index. (2) An embedded exploratory qualitative study using semistructured indepth interviews (n=3–4 physiotherapists) and a focus group (n=6–8 patients) and entailing the recruitment of purposive samples will explore perceptions of the ABPI. Quantitative data will be analysed descriptively. Qualitative data will be coded and analysed deductively (identify themes) and inductively (identify additional themes).

Ethics and dissemination This trial is approved by the University of Birmingham Ethics Committee (ERN_15-0542).

Trial registration number ISRCTN84528320.