The defence of mental illness is provided for under the Mental Health (Forensic Provisions) Act 1990. If at the time of the offence the accused was mentally ill, the law will not hold them criminally liable. The jury will return a special verdict of “not guilty by reason of mental illness” and the court may order that the mentally ill person be detained in such place and in such manner as the court thinks fit.
To establish that the accused was mentally ill so as not to be responsible their acts or omissions, the accused must show that:
- As a result of a ‘defect of reason’ from a ‘disease of the mind’, the accused did not appreciate the nature and quality of that physical act, i.e., that the accused did not know what they were doing was wrong.
A ‘disease of the mind’ which produces a ‘defect of reason’ means that the accused’s state of mind must have been one of disease, disorder or disturbance arising from some condition which may be temporary or of long standing, whether curable or incurable.
The onus of proof
The onus of proof for the defence of mental illness falls on the accused to establish on the balance of probabilities. This means that the accused must prove that it is more likely than not that they were mentally ill at the time of the committing the criminal offence.