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The effect of mistake

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Mistake of Law

‘Ignorance of the law excuses no one’

Arrowsmith (1974) CA

Distributed leaflets to British soldiers. Previously the DPP had declined to prosecute. He thought this was all right.


Held: Guilty of inciting disaffection. Mistake of law would not avail.



Ignorance of law - exception to usual rule where statute requires knowingly = OK, but only civil law requirements

Secretary of State for Trade and Industry v Hart (1982)

D acted as auditor of two companies of which he was director.


Held: Not guilty. Under the statute, a person in his position must be aware of the statutory restrictions. He was entitled to rely on ignorance of the law as a defence, in contrast to the usual practice and the usual rule. The statute gave him that right.


Not guilty

But not unless in statute

Grant v Borg (1982) HL

Remained in UK beyond the time limit granted.


Held: Not guilty [on other grounds]. To argue that "knowingly" in a criminal statute required not merely knowledge of the facts but also knowledge of the relevant law, would be revolutionary and ... wholly unacceptable.'



Mistake as to FACT and inadvertence (carelessness, or recklessness) consist of a denial of the mens rea

Mistake as to the actus reus e.g. relevant facts

As thought by the defendant (subjectively).

Tolson (1889) CCR

No longer good law (B (a minor) v DPP

D remarried five years after last seeing her husband, believing him lost at sea. In fact he had deserted her and was still alive.


Held: Not guilty of bigamy. She believed 'in good faith and on reasonable grounds' that her husband was dead.


Not guilty

B (a minor) v DPP [2000]




[General defences – mistake – need for subjective test]

D aged 15 years, sat next to a girl aged 13 years on a bus in Harrow. He asked the girl several times to perform oral sex with him. She repeatedly refused. He was charged with inciting a girl under 14 to commit an act of gross indecency contrary to section 1(1) of the Indecency with Children Act 1960. Section 1(1).

He claimed that he had believed the girl to be over 14


Held: In a number of recent cases in which a defence of honest but mistaken belief had been raised, the courts had placed new emphasis on the subjective nature of the mental element. As a matter of principle, this ‘honest belief’ approach was preferable.

By definition, the mental element in a crime was concerned with a subjective state of mind.

"Is there here a compellingly clear implication that Parliament should be taken to have intended that the ordinary common law requirement of a mental element should be excluded in respect of the age ingredient of the new offence? Thus far, having regard especially to the breadth of the offence and the gravity of the stigma and penal consequences which a conviction brings, I see no sufficient ground for so concluding."

Not guilty

The law will never require that the mistake have been reasonable, provided it was honestly held and Tolson is now bad law.

Thabo Meli v R (1954) PC

D1 and D2 conspired to murder V. Struck V over the head. Believing him dead, they rolled his body over a cliff. V died of exposure while unconscious.


Held: D1 and D2 are guilty of murder.



Church (1965) CCA

Defendant claimed to have taken girl to a van for sex. In the van she mocked him and slapped him. Fight followed when he knocked her unconscious. Unable to revive her, panicked, dragged her out of the van and into a river.

The girl drowned.


Held: Guilty of manslaughter. A series of acts that culminated in her death and thus constituted manslaughter. The unlawful act must be such as all sober and reasonable people would inevitably recognise must risk of some harm.



Honest belief as to actus reus, OK in some situations. Honest belief only needed; irrelevant that it is unjustified belief.

Smith (DR) (1974) CA

During his tenancy built panelling to conceal some wires. He removed the panelling when his tenancy ended.


Held: Not guilty of criminal damage. Although the property was the landlord's, D honestly but mistakenly believed the property was his own. Provided that the belief is honestly held, it is irrelevant whether or not it is a justifiable belief.


Not guilty

But honest mistake not OK in other situations (sexual offences and rape)

Morgan (1976) HL


Defendant invited several companions to have sexual intercourse with his wife. Told them that her resistance would not constitute lack of consent but rather enhanced her satisfaction.


Held: D was guilty of aiding and abetting rape. The companions were guilty of rape. Mistake as to V's consent must be honest but need not be reasonable. No room for either a 'defence' of honest belief or mistake.



(The House of Lords upheld the convictions on the basis that the accused had not actually held any mistaken belief.)

Subjective awareness

Thus one can generalise that wherever an offence requires subjective awareness of a particular element, a genuine mistake that such an element is absent will be a defence.


Again. Honest mistake as to actus reus, OK in yet different situations

Williams (Gladstone) (1984) CA

D saw a man assaulting a youth. The youth was calling for help. The man was in fact affecting a lawful arrest of the youth, albeit falsely claiming to be a police officer. D intervened


Held: D was not guilty of assault. He honestly believed that he was preventing an unlawful assault. If the belief was in fact held, its unreasonableness is neither here nor there. It is irrelevant.


Not guilty

Mistake whilst voluntary intoxicated,

Hopeless plea, especially in murder

Even if an honest mistake, which would otherwise succeed

O'Grady (1987) CA

D was drunk when he struck and cut V, causing his death. He mistakenly believed V was attacking him with a glass.


Held: Guilty of murder.

(1) So far as self-defence was concerned, reliance could not be placed on a mistake of fact induced by voluntary intoxication.

(2) Per curiam: A sober man who mistakenly believes he is in danger of immediate death should be acquitted if his reaction in killing his supposed assailant was a reasonable one.


Probably not now required to be reasonable if honestly held.

Self defence - amount of force

Objectively judged, by the jury

Beckford v R (1987) PC

A police officer investigating a domestic dispute at a house, shot and killed a man who ran out of the back of the house.


Held: D was not guilty of murder.

The test to be applied for self-defence is that a person may use such force as is reasonable in the circumstances, as he honestly believes them to be in the defence of himself or another.


Not guilty

Owino [1995]

[General Defences - Mistake]

D a senior registrar in microbiology,
Fractured his wife’s wrist
Gave her a black eye,
Hit her about the head causing possible damage to her eardrum, threw her out of the flat, injuring her right thumb,
Lifted her up and put her out of the house.
In relation to counts 3 and 4, self-defence was raised.


Held: the test of the appropriate degree of force a person was entitled to use in self-defence was not any degree of force which he believed was reasonable, however well-founded the belief.

A jury must decide whether a D honestly believed that the circumstances were such as required him to use force to defend himself from an attack or threatened attack. A D must be judged in accordance with his honest belief, even though that belief may be mistaken.

But the jury has then to decide whether the force used was reasonable in the circumstances, as he believed them to be.

A belief that the degree of force he was using was reasonable will not enable him to do what he did.

"If that argument was correct, then it would justify, for example, the shooting of someone who was merely threatening to throw a punch, on the basis that the D honestly believed, although unreasonably and mistakenly, that it was justifiable for him to use that degree of force. That clearly is not, and cannot be, the law."


There are problems with this concept of reasonableness, particularly with regard to manslaughter. The belief in the level of force to be necessary is subjective, yet the test for manslaughter is objective. The two do not sit comfortably together.

God is not available as a defence in common law

Or as defence of duress - too remote

Remoteness of acts intended to prevent

Sincerely held beliefs do not make an act lawful: no defence

Blake v DPP (1993)

A vicar wrote a biblical quotation on a concrete pillar to protest against the Gulf War. He claimed to have the consent of God.


Held: Guilty of criminal damage. (1) Divine command is not a lawful excuse under the common law. (2) The act was not capable of protecting property in the Gulf States, as it was too remote. (3) Defence of necessity or duress unsuccessful, as divine command did not, objectively speaking, create an immediate danger or fear of danger.



Morrow Geach and Thomas (1994)

Three defendants planned and carried out an anti-abortion demonstration outside a clinic. Caused severe distress to patients.


Held: Guilty of offences under the Public Order Act 1986. Notwithstanding the sincere and deeply held opinions of the defendants. The three were guilty of unreasonable disorderly conduct.



Threat of war

Even honest belief of a threat of war is not available

There have been several attempts to use the illegality of war or other anti-war arguments to justify committing actions that would otherwise be an offence, this argument normally fails, for example R v Jones (Margaret) [2006] HL (Conjoined Appeals).


R v Jones involved various acts of protest by 20 different defendants at an RAF and US Air Force base, a military port and other locations where they committed acts of aggravated trespass and criminal damage.  They did this in the honest belief that the 2003 war against Iraq was illegal.  Their argument included their right to commit comparatively minor acts to prevent a greater crime in Iraq; but the HoL decided that there was no crime under English domestic law to justify conduct on the ground that they were preventing a “crime” within s 3 of the 1967 Act (or “an offence” under section 68 Criminal Justice and Public Order Act 1994).


The two Acts were domestic in nature and the courts no longer had power to create new offences; as a matter of democratic principle it was for Parliament alone to do so.


Defences using this argument are often categorised under the defence of "mistake" as the defendant was acting under a mistake of law.


See Blake v DPP (1993) DC.


Concluding thoughts

Is this like subjective and objective recklessness?

Sort of…

It would seem that the position as regards mistake in crimes of recklessness can best be summarised as follows.

A genuine mistake is a defence to rape Satnam (1983) and indecent assault R v Kimber [1983] and to any other crime of subjective (Cunningham) recklessness.


Crimes requiring Caldwell recklessness appear to be governed by a harsher rule that the accused has a defence only if he has totally ruled out the risk of the relevant consequence occurring.


If the risk is ruled out to the extent that all that remains is a risk that "an ordinary prudent individual would feel justified in treating . . . as negligible", that should, in principle, be sufficient. However, in Merrick [1996], the Court of Appeal continued to speak of ‘preventing the risk [from arising] at all’.


It was not sufficient to remedy a risk that the accused had already created as opposed to preventing the risk from arising in the first place. Only the latter would take the accused outside the Caldwell definition.



  • The test of a mistake to defend oneself is a subjective test; ‘is it an honestly held belief?’

  • The test of mistake as to the amount of force used is an objective test, judged by a sober and reasonable person.

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