Insanity : defined in the M'Naghten Rules (1843) as "It must be clearly proved that, at the time of committing the act, the defendant was labouring such a defect of reason, from disease of mind as to not know:
If a person is found not guilty by reason of insanity the court may instead give treatment order, hospital order, secure hospitals. And in some more severe cases they may spend the rest of their lives in a secure hospital as they are deemed a threat to society