Where the defendant acts under a mistaken belief of the circumstances they may be afforded the defence of mistake. Where a defendant acts under such a mistake, the mistake prevents them forming the mens rea of the crime and thus mistake is not really a defence as such, but relates to the absence of the elements of establishing liability. The defence of mistake was first recognised in R v Tolson (1889) 23 QBD 168 but has developed since then. Often the defence of mistake is complicated by being combined with other defences such as intoxication or self-defence (or both).
Controversy rages as to whether mistake should even be regarded as a category of defence in its own right. This was a point stressed by Lord Hailsham in DPP v Morgan. Herring asserts:
“Rather, a mistake can be a particular way of denying that a defendant has mens rea or asserting that the defendant has a defence such as self-defence.”
However, Smith & Hogan expresses the view that the “landmark” decision of Morgan settled the principle that mistake is a defence where it prevents the defendant from having the mens rea which the law requires for the crime with which he is charged. The operation of mistake as a defence will differ according to the requirements of the offence. Thus where intention or recklessness is required, mistake may operate as a defence whereas if only negligence is required, it is only a reasonable mistake which can provide a defence since a reasonable man would not, by definition, make a mistake.
A mistake may negate mens rea. If a defendant honestly believed that he was shooting a fox but mistakenly shot a hunt saboteur who died from his wounds, the mistake would provide a defence to murder. This is not to say that mistake per se provides the defence: in such a situation, it is the lack of mens rea. By contrast, there are circumstances in which a mistake has occurred but the mens rea is still present. Thus, if the hunt saboteur intends to shoot the Master of Hounds but mistakenly shoots a member of the public in a pink jacket, the mistake will not assist in defence since there was in any event the intent to kill a person. A mistaken belief may form the basis of a defence: if a huntsman honestly believed that a saboteur was about to kill him and stabbed him dead, there would clearly have been a mistake but it is the defence of self-defence that operates. Finally, there can be mistakes of law but the principle ignorantia legis haud excusat (ignorance of the law is no excuse) will apply. Therefore, if a huntsman genuinely believed as a result of propaganda from the Countryside Alliance that it remained legal to hunt with hounds and did so, the mistake would not afford a defence. On balance, therefore, despite the fact that mistake remains a familiar category in textbooks on Criminal Law, it is possible to take issue with Smith & Hogan since it can be demonstrated that in every instance in which a mistake leads to the commission of an offence, if a defence is available it is available on grounds other than the mistake itself.
Conversely, Smith & Hogan (at p.239) asserts that “intoxication is not, and never has been, a defence in itself”. A leading case on intoxication is Kingston in which the defendant was involuntarily intoxicated and committed an act of paedophilia. While he admitted such tendencies, he claimed that he was usually able to keep them under control. The Court of Appeal held that if drugs were surreptitiously administered to a person who was thereby caused to lose his inhibitions and form an intent which he would not otherwise have formed this was not a criminal intent. However, for the House of Lords this was “a bridge too far” and Lord Mustill reaffirmed the principle that if a defendant has the necessary mens rea for an offence but he only committed it because he was involuntarily intoxicated, there is no defence.
Beard established that intoxication was only a defence if it rendered the defendant incapable of forming the necessary mens rea. This was followed by the leading case of Majewski in which the House of Lords held that evidence of self-induced intoxication is a defence to an offence requiring specific intent but not to any other type of offence. However, what has come to be known as the ‘MajewskiRule’has been held to be inapplicable where statute provides that a particular belief is capable of forming a defence. For example, s.5(2) of the Criminal Damage Act 1971 provides that a belief that a person would consent to damage is a defence to criminal damage. Thus in Jaggard v Dickinson, the defendants caused criminal damage while breaking into a house which, while drunk, she mistakenly thought belonged to a friend of hers who would have consented to her entering in this way. The offence of criminal damage does not require specific intent and therefore the defendant could not have relied upon her drunkenness as a defence but it was nonetheless allowed as an explanation of the state of her belief in mounting the statutory defence under the Act. The court in Jaggard was careful to distinguish between allowing the defence to operate in this way and allowing intoxication as a means of rebutting intention or recklessness. While this can be justified by a narrow interpretation – relying upon the specific statutory defence provided by s.5(2) – this would appear to be a distinction without a difference.
Once again, however, it can be seen from the foregoing examples that in cases in which the issue of intoxication is raised, the focus is not upon intoxication as a defence (or lack of it) in itself but rather upon whether the factor of intoxication is capable of negativing the requisite mens rea. Thus in the case of both mistake and intoxication, while these are both familiar categories of the generic term ‘defence’, it must remain highly doubtful that they are defences in their own right. To be fair, however, if this analysis is extended to many other categories of so-called defence – for example, provocation, duress and diminished responsibility – the same criticism might be levelled. It might therefore be more constructive in almost every case to pose the question as to whether mens rea is present rather than attempting artificially to “pigeon-hole” the facts of a particular case into one or other categories of defence so-beloved of the authors of the Criminal Law texts.