Mental illness is common: at least 20 per cent of adults suffer from it at any one time. Depression and anxiety disorders are the most common conditions and they reduce life satisfaction by 0.7 points (out of 10). In the UK the health watchdog NICE recommends that all patients are offered psychological therapy. Until 2008 almost none were, but since then, NHS Talking Therapies (NHSTT) has treated some eight million patients of whom half have recovered during therapy. Many have gone back to work and the service brings more money into the Exchequer in taxes paid (and benefits not paid) to more than cover the original cost of the therapy. This happens within two years of the end of treatment. There are also important reductions in the use of NHS physical healthcare services.

But the service does not cover people suffering from addiction, personality disorder or other severe mental illness. This chapter evaluates provision of psychological therapy on a large scale to those people. It concludes that this provision too would pay for itself within two years.