1. Possible answer.
Insanity is a general defence to ALL crimes whereas diminished responsibility is a special and
partial defence to a charge of murder ONLY.
The DEFENDANT must prove that he or she was suffering from insanity when he or she
committed the offence. This must be proved on the BALANCE OF PROBABILITITES. Critics
have argued that this is unfair in that it undermines the notion that the defendant is
innocent until proven guilty by the prosecution. The Butler Committee and the Criminal Law
Revision Committee have suggested that, since it is part of mens rea, the burden of proof
should be reversed and placed on the prosecution rather than the defendant
When the D is found to be insane the verdict is ‘not guilty by reason of insanity’.
Until the introduction of the Criminal Procedure Act 1991, this automatically meant an
indefinite hospital stay and meant that defendants were particularly reluctant to plead
insanity, but now this only applies to murder.
If the defendant is charged with another crime, the judge can make a hospital order, a
guardianship order, supervision and treatment order, or an absolute discharge. If D is
charged with murder then the judge must impose an indefinite hospital order. The home
secretary must consent to release.
In the case of McNaghten, it was held that ‘the jurors ought to be told in all cases that every
man is presumed to be sane, and to possess a sufficient degree of reason to be responsible
for his crimes, unless proved that he was labouring under such a defect of reason, from
disease of the mind, as not to know the nature and quality of the act he was doing, or, if he
did know it, that he did not know he was doing what was wrong.
The three elements:
Defect of reason
D must show that his or her ability to reason was impaired. The basis of the defence is the
defendant’s deprivation of the power of reasoning. A defendant who still possessed the
powers of reasoning but failed to use them cannot be classed as insane. In Clarke (1972) it
was held that Defect of reason must be more than absent mindedness or confusion.
Disease of the mind
This is a legal term and not a medical one. The problem with this have been made apparent
by the types of conditions that the courts have accepted as constituting a disease of mind,
such as arteriosclerosis (Kemp) , epilepsy (Sullivan) and diabetes (Hennessy). These decisions
have illustrated the fact that the definition is purely legal which has been broadened to
cover the operation of the mind in all its aspects.
Under this element, the reluctance to accept automatism as a full defence if it could mean
releasing potentially dangerous people back into society is in issue. The general rule is that if
automatism (acts done by the muscles without any control by the mind) is caused by a
‘disease of the mind’ then the M’Naghten rules apply and the D will be found not guilty by
reason of insanity. (Insane Automatism). Where the automatism is caused by an external
factor then the defendant will be found not guilty as none-insane automatism is a complete

2. defence. The question of whether D’s condition is sane or insane automatism is one of law
for the judge (Bratty 1963). The continuing danger theory focuses on the danger or
recurrence. If there is a danger of recurrence then the more likely a condition will be treated
as a disease of mind. (Burgess 1991). The external cause theory focuses on the cause of the
automatism and says that conditions stemming from the psychological or emotional makeup
of the accused, rather than from some external factor, should lead to a finding of insanity
The application of these theories has caused problems of inconsistency as can be
demonstrated in the diabetes cases of Hennesy and Quick.
One diabetic, who fell into a hypoglycaemic state after taking insulin but not eating enough,
was acquitted because it was an external factor (the insulin) causing the seizure (Quick),
whereas another diabetic, who fell into a hyperglycaemic state, after failing to take insulin
for three days was treated as pleading insanity as it was the disease itself (an internal factor)
causing the seizure (Hennessy). The decision in quick is generally regarded as incorrect.
Although the insulin was caused the state, the underlying cause was his diabetes.
Consistency requires that any diabetic seizure should be regarded as a disease of the mind. If
found insane, the defendant will not necessarily face hospitalisation after the passing of the
1991 Act and may simply be subject to a supervision or treatment order or may be
discharged. However, the classification of diabetics, epileptics and sleepwalkers as insane
has been criticised for suggesting that those suffering from such conditions are a danger to
the public, whereas this is far from the truth in the vast majority of cases. Most people with
such conditions are able to control them by taking medication. The social stigma that can
attach to an epileptic etc from a finding of ‘not guilty owing to insanity’ can be far reaching.
In addition to the criticisms related to the broadness of this legal definition, critics have
argued that it is also out of date. It dates from 1843 and fails to take account of the huge
medical advances that have occurred since then.
D Did not know the nature and quality of the act.
It must also be proven that in terms of the ‘nature and quality of the act’, the defendant
would be unaware of his or her actions. D must not know that what he was doing was legally
wrong. (Windle).
This element of the rule as been criticised for making the defence too narrow as it can rule
out those who are medically insane if they know the nature and quality of their act or that it
is legally wrong but are nonetheless unable to stop themselves from committing it. Thus,
those at whom the defence should be aimed are unable to rely on it. For example in the case
of Byrne. He was a sexual psychopath who could not resist perverse ideas. He knew what he
was doing was wrong and so couldn’t rely on the defence of insanity but could rely on the
defence of DR instead. But DR only available for a charge of murder!
Other evaluation points include the fact that the defences are effectively established or
rebutted by medical experts rather than being decided upon by jurors. It is argued that
doctors should not be delivering opinions on legal or moral responsibility which are
essentially jury issues
There is also potential for jury confusion & misapplication owing to emotional
considerations, sympathy or crude ‘gut reaction’. For example in the Peter Sutcliffe – the

3. ‘Yorkshire Ripper’ case where psychiatrists were unanimous in agreeing he was a paranoid
schizophrenic yet he was convicted of murder.
A new defence
Critics argue that the only way forward is to abolish the M’Naghten rules altogether. Instead,
a new defence should be introduced. The Butler Committee suggested that this should apply
to defendants with a mental disorder and should result in a verdict of ‘not guilty on evidence
of a mental disorder’. In 1989 the Law Commission’s Draft Criminal Code proposed that a
defendant should not be guilty on evidence of severe mental disorder or severe mental
handicap. This would avoid the defendant being labelled insane. Others suggest that there is
no need for such a defence at all and that those suffering from insanity should be dealt with
outside the criminal justice system.
In light of the above exploration of the defence of insanity, it would seem apt to agree with
the statement that it is outdated and unsatisfactory and with the opinion that reform is long
overdue in the interests of both justice and common sense. It is founded on legal rather than
medical definitions, and this legal definition was established in a time of limited medical
knowledge. This has led to unsatisfactory and inconsistent decisions, labelling insane those
who are suffering from a physical medical condition which seems to go against common
sense and justice. The burden upon the defendant to prove that he is insane goes against a
fundamental principle of the criminal law that we are innocent until proven guilty. Despite
the changes in terms of orders that can be made by a judge finding a defendant not guilty by
reason of insanity after the 1991 Act, the defence remains unsatisfactory and in desperate
need of reform.