The insanity defence
A question about their state of mind at the time of the act, under rules from 1843.
What is the insanity defence?
The insanity defence is about the person's state of mind when they acted. If it succeeds, the jury returns the special verdict: not guilty by reason of insanity (1964 Act s1).
Everyone is presumed sane, so the defence must prove insanity on the balance of probabilities. It isn't limited to murder: Keal (2022) was a trial for attempted murder. Nor must it be permanent: juries are told insanity may be temporary and curable.
The M'Naghten Rules
The test dates from 1843. The defence must show that, at the time of the act, the person had:
- A defect of reason. Losing self-control isn't enough. An irresistible impulse is no defence (Kopsch, 1927, followed in Keal).
- From a disease of the mind. This is a legal idea, not a diagnosis. Courts have counted epilepsy, hyperglycaemia and sleepwalking.
- So they didn't know. Either they didn't know the nature and quality of the act, or they didn't know it was wrong.
Delusions are judged as if the facts in them were real. Someone who kills believing, through a delusion, that they're being attacked may have the defence. Someone who kills in revenge for an imagined injury doesn't (M'Naghten's fourth answer, set out in Keal).
What does 'wrong' mean? Windle and Keal
In Windle (1952), a man who killed his wife knew the law forbade it but thought it was right. The defence failed, because he knew it was against the law.
Keal (2022) settled the wider point. 'Wrong' means both against the law and wrong by the standards of ordinary reasonable people. The defence has to show the person knew neither, so knowing either defeats it.
Keal also held that believing you had no choice doesn't help if you knew the act was wrong. His case was that a delusion of possession by the devil compelled him.
The special verdict: what happens next
- A hospital order, with or without restrictions.
- A supervision order, for up to 2 years.
- An absolute discharge, where the court thinks that most suitable (s5(3A)).
- Murder. If a hospital order is possible, it must be made with restrictions (s5(3)).
These are the same disposals as after a finding of unfitness (1964 Act s5). So is insanity a complete defence? It answers the charge in full, but it isn't an ordinary acquittal: the Act says 'verdict of acquittal' doesn't include the special verdict (s8(2)).
Insanity vs diminished responsibility vs fitness to plead
| Insanity | Diminished responsibility | Fitness to plead | |
|---|---|---|---|
| The question | Did they know what they were doing, or that it was wrong, when they acted? | Did an abnormality of mental functioning substantially impair them when they killed? | Can they take part in their trial now? |
| Applies to | Not limited to murder | Murder only | Any Crown Court trial |
| Who proves it | The defence, on the balance of probabilities | The defence, on the balance of probabilities | Whoever raises it |
| Result | Special verdict, then hospital, supervision or discharge | Manslaughter, with the full range of sentences | A trial of the facts, then the same disposals as insanity |
At a murder trial, if the defence raises insanity or diminished responsibility, the prosecution can bring evidence of the other (1964 Act s6). See fitness to plead and diminished responsibility.
Reform, and other countries
The Law Commission's 2013 discussion paper proposed reform, including a test based on lacking the capacity to control your actions. In Keal the Court of Appeal said any such change is for Parliament. The 1964 Act extends only to England and Wales (s8(4)), so the US, Canada, Australia and Scotland have their own law.
The rules in brief
- The test (M'Naghten Rules). A defect of reason, from a disease of the mind, such that they didn't know the nature and quality of the act, or didn't know it was wrong.
- "Wrong" means both against the law and wrong by ordinary people's standards. Knowing either defeats the defence (R v Windle, 1952; R v Keal, 2022). Believing it morally justified isn't enough.
- Disease of the mind is a legal idea. Courts have counted epilepsy, hyperglycaemia and sleepwalking.
- Burden. On the defence, on the balance of probabilities.
- Verdict. Not guilty by reason of insanity. The disposals are the same as after a finding of unfitness.
Read more: CP(I)A 1964, s5 · Criminal Procedure (Insanity) Act 1964 - revised text
Automatism
Not reduced control: no control at all.
What is automatism?
Automatism is an act done without any control by the mind, such as a reflex, or by someone not conscious of what they're doing (Bratty, 1963). It isn't reduced control, but none at all. A reported blackout on its own won't establish it. What matters most is the cause, because that decides the outcome.
Sane vs insane automatism
| Sane automatism | Insane automatism | |
|---|---|---|
| Cause | External, such as a blow to the head or insulin | Internal: a disease of the mind |
| Examples | Hypoglycaemia after insulin (Quick, 1973) | Hyperglycaemia from diabetes itself (Hennessy, 1989); sleepwalking (Burgess, 1991) |
| Burden | The defence raises evidence, then the prosecution must disprove it | The defence proves it, on the balance of probabilities |
| Outcome | A complete acquittal | The special verdict, as for insanity |
So the same illness can fall on either side. A person with diabetes who has a hypo from their insulin has an external cause. One whose blood sugar runs high from the diabetes itself has an internal one.
Is automatism a complete defence?
Sane automatism usually is: the result is a complete acquittal. It can fail if they brought it on themselves, through drink or drugs, or recklessly, say by skipping food after insulin (Bailey, 1983). Insane automatism leads to the special verdict instead, and then a hospital order, a supervision order or an absolute discharge. So the cause decides whether the person is acquitted outright, or the court has to choose a disposal.
The evidence the court wants
- Corroboration. Witnesses, records or an EEG, not just a reported blackout.
- The mechanism. Say what you think caused the episode, internal or external, and how confident you are.
- The label is legal. Whether it was a disease of the mind is for the court. Give it the medical facts it needs to decide.
- Your limits. If the question needs a neurologist or a sleep specialist, say so (CrimPR r19.2). See psychiatric reports for court.
A worked example
A man with type 1 diabetes injects his insulin and, an hour later, punches a stranger at a bus stop. Witnesses say he looked dazed and sweaty, and paramedics recorded a very low blood glucose.
This points to sane automatism: an external cause, the insulin, with corroboration from the witnesses and the glucose reading. Once the defence raises it, the prosecution has to disprove it, or show he brought it on recklessly, say by skipping food. If it can't, he's acquitted. Had his sugar been high from the diabetes itself, it would be insane automatism and the special verdict.
What the MRCPsych asks
Expect the classic pairs. Hypoglycaemia from insulin is external and sane (Quick). Hyperglycaemia from diabetes is internal and insane (Hennessy). Sleepwalking is insane automatism (Burgess). And automatism means no control at all (Bratty), not impaired control. Questions often turn on the outcome, so learn which result goes with each.
The rules in brief
- What it is. An act done without any control by the mind, such as a reflex, or by someone not conscious of what they're doing (Bratty, 1963).
- Sane automatism has an external cause, such as a blow to the head or hypoglycaemia from insulin (R v Quick, 1973). The result is a complete acquittal.
- Insane automatism has an internal cause, such as hyperglycaemia from diabetes itself (R v Hennessy, 1989) or sleepwalking (R v Burgess, 1991). The result is the special verdict, as for insanity.
- Burden. For sane automatism the defence must raise evidence, then the prosecution must disprove it. Insane automatism is for the defence to prove, as with insanity.
- Evidence. Courts want corroboration: witnesses, records or an EEG, not just a reported blackout.
Questions trainees ask
What are the M'Naghten Rules?
They're the test for insanity. A defect of reason, from a disease of the mind, meant the person didn't know the nature and quality of the act, or didn't know it was wrong. After R v Keal (2022), that means knowing neither that it was illegal nor that ordinary people would think it wrong.
What's the difference between sane and insane automatism?
Sane automatism has an external cause and leads to acquittal. Insane automatism has an internal cause and leads to the special verdict of not guilty by reason of insanity.
Is insanity a complete defence?
It answers the charge in full, with a special verdict of not guilty by reason of insanity. But the court must then choose a disposal: a hospital order, a supervision order or an absolute discharge.
How does the insanity plea work?
The defence raises it and must prove it on the balance of probabilities, with evidence from two doctors, one s12 approved, which the special verdict requires. The jury decides whether to return the special verdict.
Is temporary insanity a defence?
Insanity doesn't have to be permanent. What matters is the M'Naghten test at the time of the act, and juries are told insanity may be temporary and curable.
Is automatism a complete defence?
Sane automatism usually is, and leads to a complete acquittal. Self-induced automatism, such as from drink, drugs or skipping food after insulin, may not be. Insane automatism leads to the special verdict instead.
What's the difference between insanity and fitness to plead?
Insanity is about their state of mind at the time of the act. Fitness to plead is about whether they can take part in their trial now.
Test yourself
A man kills his neighbour. He knew what he was doing and knew it was against the law, but believed God had commanded it. Does the insanity defence apply?
Show the answer
B. Under M'Naghten, knowing the act was against the law defeats the defence (Windle, 1952). Believing he had no choice, as under a command from God, doesn't help (Keal, 2022). He knew both the nature of the act and that it was against the law, so the defence fails. Diminished responsibility may still apply.
Quick-fire
The insanity rules date from
Show the answer
1843