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. James, who's 23, has an unusual anxiety: a profound fear that he'll lose control of his bowel movements in public. Consequently he spends up to seven hours a day in the loo, too scared to leave in case he has an accident. He's been in and out of psychiatric institutions since he was a teenager and had to drop out of university because his OCD got so bad. Helen is a librarian at the British Museum. She has an irrational fear of harming strangers: she believes that somehow she's responsible for killing them in road traffic accidents or putting them in rubbish bins. For two years she's lived the life of a recluse, too worried to leave the house or go to work. Aaron is a middle manager with an oil company who struggles with perfectionism. He can spend hours opening and closing drawers or switching lights off and on, unable to stop until he's carried out the task a certain number of times. He's hidden his OCD from everyone, worried the world will think he's crazy. They're all on an intensive 12-week therapy programme at the Bethlem, which has a three in four success rate. Simon Darnley, the Head of the Anxiety Disorders Residential Unit (ADRU), says some patients can be completely 'cured'.