 Under the current law there are two applications of the insanity defence ; where it is claimed that the defendant was insane at the time that he committed the crime , and where it is claimed that he was insane at the time of the trial and thus unable to effectively defend himself . The defence is most commonly used in the Crown Court , since it was previously believed that it required a jury ; in DPP v Harper [ 1997 ] , it was decided that the defence could also be applied in the Magistrates ' Court . 
