Cognitive behavioural analysis system of psychotherapy (CBASP) is one of the only psychological models and treatments that has been designed specifically for patients diagnosed with chronic depression. CBASP in combination with antidepressants has been found to be the most effective treatment for chronic depression. Despite an increasing amount of research into this intervention, researchers are less aware of the role that specific and common ingredients are accounted for in outcomes. Given that CBASP is a treatment model endorsed by the National Health Service Scotland (NHS Scotland), gaining a deeper knowledge and understanding about the active ingredients involved in their success ensures current practice is embedded in an evidence base. Conducting this research adds to the gap in the literature and identifies areas in which further exploration is warranted. Given the emphasis on therapist variables in relation to treatment outcomes, the results of this research will have wider implications from a service resource perspective. Training may be altered or needs emphasised in line with the results of the study to ensure most efficacious outcomes.