 The Butler Committee 's report in 1975 submitted the law of insanity to intense criticism , saying that it is " based on too limited a concept of the nature of mental disorder " , noting " the outmoded language of the M 'Naghten Rules which gives rise to problems of interpretation " and that the rules were " based on the now obsolete belief in the pre @-@ eminent role of reason in controlling social behaviour ... [ the rules ] are not therefore a satisfactory test of criminal responsibility " . An additional criticism given is that the defence puts the burden of proof onto the defendant , while in all other cases the burden is on the prosecution . The Butler Committee proposed reform , which was repeatedly ignored by successive governments ; the Law Commission drafted a Criminal Code Bill in 1989 which altered the rules on insanity , but this was again ignored . 
