Using G-Power to calculate our sample size and based on a moderate between group effect size of d=0.5 with a power of 80% and a 2:1 randomisation procedure into immediate treatment for depression and/or anxiety and a corresponding waiting list control group returned a total sample of 288. Adding a 25% uplift to ameliorate against attrition gave a total sample size of 360. Therefore for depression a total sample of 120 in the treatment group and a corresponding 60 in the control group and the same ratio for anxiety disorders. The 2:1 randomisation procedure was implemented to reduce the concern of having many people waiting for treatment after presenting to the IAPT service.