ABSTRACT
A new diminished responsibility plea was introduced into English law by the Coroners and Justice Act 2009. In essence, therefore, the official view has been that the old was in need of clarification and modernisation. In doing so the Ministry of Justice concluded that it was an appropriate vehicle for reform, after parliamentary scrutiny, a new diminished responsibility plea modelled on the Law Commission's proposal, subject to the exclusion of 'developmental immaturity'. However, in much the same way as the Ministry of Justice and the government in England and Wales made changes to the Law Commission's final proposal, so did the New South Wales government. As a result the study was able to compare the operation of the original diminished responsibility plea with the new 'substantial impairment' plea. This may be contrasted with the position of the provocation plea in England and Wales where there were genuine political and policy concerns about its application.
