Where the defendant acts under a mistaken belief of the circumstances they may be afforded the defence of mistake. As the mistake prevents them forming the mens rea of the crime, mistake is not really a defence as such, but relates to the absence of an element for establishing liability. Its relevance is specific to the offence involved as it is specific to the type of mental element involved.

Sexual Offences

Initially, the mistaken belief had to be both “honestly and reasonably” held. The belief must be a reasonable belief; such as a belief “as a reasonable man would entertain if he applied his mind and thought about the matter”.

This was amended by DPP v Morgan [1976] AC 182 House of Lords. The three appellants were convicted of rape. They had been out drinking for the night with a fellow officer in the RAF who invited them back to his house to have sexual intercourse with his wife. According to the appellants, he had told them that his wife would be consenting, although she would act protest. At appeal, it was concluded the belief must be genuine and honest, but there was no requirement that the belief was reasonable. The convictions were upheld, however, as the House of Lords was of the opinion that no jury properly directed would have considered the belief of the defendants in the circumstances as genuine.

The “Morgan defence” was abolished by the Sexual Offences Act 2003, which requires a “reasonable belief in consent”. Deciding whether a belief is reasonable is to be determined having regard to all the circumstances, including any steps (A) has taken to ascertain whether (B) consents. The test of reasonable belief is a subjective test with an objective element. The best way of dealing with this issue is to ask two questions:

1. Did the defendant believe the complainant consented? (subjective element)
2. If so, did the defendant reasonably believe it? (objective element).

As offences in the Sexual Offences Act 2003 are crimes of basic intent, voluntary intoxication is not a defence (R v Fotheringham (1989) 88 Cr App R 206).

B v R. [2013] EWCA Crim 3 addressed this in regard to delusional belief. The appellant, who suffered from paranoid schizophrenia, aggressively insisted on having intercourse with the victim. He was suffering from paranoid schizophrenia. Lord Justice Hughes took the view

“if… the defendant’s delusional beliefs could have led him to believe that his partner consented when she did not, we take the clear view that such delusional beliefs cannot in law render reasonable a belief that his partner was consenting when in fact she was not… A delusional belief in consent, if entertained, would be by definition irrational and thus unreasonable, not reasonable.” He concluded that “unless and until the state of mind amounts to insanity in law… beliefs in consent arising from conditions such as delusional psychotic illness or personality disorders must be judged by objective standards of reasonableness and not by taking into account a mental disorder which induced a belief which could not reasonably arise without it.”

Thus, the appeal failed on the objective element of the test of reasonable belief.

In his judgement, Lord Justice Hughes did not attempt to foresee circumstances which might arise in which a belief might be held which is not in any sense irrational and is relevant to whether his belief in consent was reasonable, even though most people would not have held it.

“Whether (for example) a particular defendant of less than ordinary intelligence or with demonstrated inability to recognise behavioural cues might be such a case, or whether his belief ought properly to be characterised as unreasonable, must await a decision on specific facts. It is possible, we think, that beliefs generated by such factors may not properly be described as irrational and might be judged by a jury not to be unreasonable on their particular facts”.

The possibility that fresh medical evidence of an Autistic Spectrum Disorder may have been relevant to a defendant’s belief in consent was accepted in R v Sultan [2008] EWCA Crim 6. Sultan appealed against a conviction of rape with fresh medical evidence that he was suffering from ASD. A retrial was ordered as this new evidence “enabled a defence for the first time to be based on the requirements of mens rea”. 

Criminal Damage

Where a statute (e.g. Section 5(2)(a) Criminal Damage Act 1971) provides a limited defence based on a genuine belief, the mistake may be relied on even where the mistake was induced by voluntary intoxication: Jaggard v Dickinson [1981] 1 QB 527.

Jaggard was told she could stay at a friend’s house. On returning home drunk, she attempted to gain access to a house she believed was her friend’s house. After being denied access by the owner, she broke a window to get inside. On appeal, it was determined a defendant was entitled to rely on mistake as a defence under s5(2)(a) Criminal Damage Act 1971 which provides that it is a lawful excuse for a person committing criminal damage that they believed the person who owned the property in question would have consented. This was the case despite the defendant’s state of intoxication.