When forensic psychiatrist Frank Farnham first meets a stalker, he doesn't judge. Some of his clients have done awful things. They have intimidated, pursued and terrified their victims. They have sent harassing emails to ex-partners or followed work colleagues home from the office. They have developed harmful fixations on people who have no intention of returning their attentions. All of them will have run the risk of being sent to jail.

But Farnham sees them, first and foremost, as people in need of his help. "They're in a real pickle," he says. "They've got in a terrible situation and can't get out of it. They can't stop."

Farnham is the co-founder of the United Kingdom's first-ever National Stalking Clinic, based at Chase Farm Hospital in Enfield, north London. The clinic, which opened in late 2011, is situated in a series of anonymous modern rooms set behind the imposing, late-Victorian facade of the hospital itself. The uninspiring setting belies the important work that goes on behind the air-locked security doors.