Anxiety has become the mental illness of our time. The NHS issues around seven million tranquiliser prescriptions every year. At the Bethlem Royal Psychiatric Hospital in South London, a specialist anxiety unit treats some of the most extreme cases in Britain: the top one per cent. Most suffer with extreme OCD.

Lambeth Hospital has pioneered the use of short-stay emergency wards for patients in crisis. It's run like A&E but for people with mental illness. Cameras are granted access for the first time to a world where psychiatrists and nurses take critical decisions about risk every day. Over the course of a few days clinicians assess whether patients are stable enough to return home or if they need to go on to a longer stay psychiatric ward. Most patients are considered a danger to themselves or others.

Fifty years ago you'd hardly ever see someone with a mental illness out and about; they were locked away in Victorian-style asylums. Today, in South London, almost 10 times more patients are cared for in their homes than in hospital. It's better known as care in the community but our perception of whether it works is often coloured by isolated stories about schizophrenics who have killed. The reality is different.

The final episode of the series visits a psychiatric ward for over-65s at the South London and Maudsley. According to psychiatrist Professor Robert Howard, 'In society old people and people with mental health problems come right at the bottom of the heap really. So, if you are old and you have got mental health problems, you have got this sort of dreadful double whammy of disadvantage.'