• Where a person acts under a mistaken belief of the law, there is no defence available for a criminal charge. Where a person however acts on a mistaken understanding of the facts, he will have a defence in mens rea. R v Bailey: ships captain was prosecuted successfully for failing to uphold the provisions of a statute passed while he was away at sea. Rogers v Louth CoCo: not correct to say that everyone is presumed to know the law. The harshness of this rule can be mitigated by the inclusion of the absence of mistake as an element of the offence. People (AG) v Grey: accused honestly believed that he was entitled to take batteries and connectors under the terms of a contract which allowed for the provision of gas for domestic purposes, but the contract did not allow him to take the goods. Ct held that the honest belief in his entitlement entitled the accused to an acquittal. Someone operating under a mistake of fact will not generally be liable, because, although d has committed the actus reus of the offense, d may honestly believe in a set of facts that would prevent him or her from forming the requisite mens rea required to constitute the crime. DPP v Morgan: RAF officer told three other officers to have sex with his wife, and that she would pretend to refuse just to be stimulating. They pleaded mistake, and the jury did not believe them. HOL held that the judge had wrongly directed the jury that the mistake must be a reasonable one; the correct legal test was whether the defendants had honestly believed the wife was consenting, not whether they reasonably believed this. However, on the facts the House of Lords held the conviction was nonetheless safe despite the misdirection. An exception is bigamy (R v Tolson).