The part respectively played by the medical expert and the court in deciding upon the criminal’s responsibility is one of the most controversial issue. In most common law countries, it appears that the jury is allowed to ignore the findings of the medical expert. In the case R v. Bryne, Per Lord Parker argued that the ‘mental responsibility of a person for his acts’ points to a consideration of the extent to which the accused person’s mind is answerable for his physical acts which must include a consideration of the extent of his ability to exercise will power to control his physical acts. For him the question is therefore to what extent the abnormality in a particular circumstance substantially impaired the mental responsibility of a person for his acts.

A further argument is that the question of degree of essentially one for the jury. He press go on his argument and says that medical evidence is relevant, but as the question involves a decision not merely as to whether there was some impairment of the mental responsibility of the accused for his acts but whether such impairment can properly called ‘substantial’, the jury may quite legitimately take different position from doctors. The argument goes on and says after all claiming that, there is no scientific measurement of the degree of difficulty, which an abnormal person finds in controlling his impulses. These problems which in the present state of medical knowledge are scientifically insoluble, the court can only approach in a broad, common sense way.

Sub-art.(3) of Art.51 on the other hand seems to put a clear boundary between the roles of the court and the medical expert in determining irresponsibility.  The court therefore may not substitute itself for the expert and adjudicate medical questions, to which he is not qualified to decide. Instead, the provision required the court to be bound to the ‘definite scientific findings’, in the sense that, if the expert states that the accused is a chronic alcoholic or a pyromaniac, it may not ignore this statement in making its decision. If the judge is allowed to disregard scientific findings to which he is not qualified to appreciate, some say he would at once be entitled to convict an irresponsible offender merely because the latter committed, in the judge’s opinion, an atrocious crime demanding punishment.

The same is true with the role of the medical expert. He/she may not substitute himself/herself for the court and adjudicate legal questions, to which he is not qualified to decide. It is, therefore, for the court to draw the “legal inferences” from the expert’s findings, so that if the expert states the accused is not fully responsible and should accordingly sentenced to, say, a punishment reduced by one half, the court is not bound by this statement.