Chronic low back pain (CLBP) is very common and causes much pain and disability. It costs the NHS billions of pounds in treatment every year and is the second leading cause of time off work. There are various treatments for CLBP, but the most effective are still only moderately helpful. Most people with CLBP receive physiotherapy, with varying results. Cognitive behaviour therapy (CBT) may offer more long term help than current treatments because it enables people to self-manage their condition. A new type of CBT, called Acceptance and Commitment Therapy (ACT), has produced particularly good results for chronic pain. However, a shortage of clinical psychologists means that most patients never receive CBT. Physiotherapists can successfully use CBT techniques with extra training, but this is not standard practice and ACT-based physiotherapy treatment has never been tested.