R (P) v MHRT East Midlands and North East Region  EWCA Civ 697
Psychopathic disorder can persist for years without causing any abnormally aggressive or seriously irresponsible conduct; it is enough that the disorder of mind has done so in the past and that there is a real risk that, if treatment in hospital is discontinued, it will do so in the future.
See also R (P) v MHRT East Midlands and North East Region  EWCA Civ 260 (permission to appeal to CA)
A change made by the Mental Health Act 2007 is related to this case. See Appropriate treatment test replaces treatability test and applies to all patients under long-term detention 3/11/08