‘Ignorance of the law is no defence,’ so we are told from an early stage in our legal studies. Or, to be more accurate, ‘ignorance of the criminal law is no defence to a criminal charge.’ That appears to be the rule in this country, apart from a couple of well-established exceptions and another possible one. I will argue that it is a preposterous doctrine, resting on insecure foundations within the criminal law and on questionable propositions about the political obligations of individuals and of the State. In developing these arguments, I will draw attention to the differing problems of ignorance of the criminal law in three broad areas – regulatory offences, serious crime, and offences of omission – with a view to suggesting that there is a great deal more that the State needs to do if the issue of ignorance of the criminal law is to be dealt with adequately and fairly.

I begin by scrutinising the relevant rule of English criminal law and the justifications offered for it. I then go on to situate the ‘ignorance-of-law’ doctrine in the context of the principle of legality and the rule of law, those bastions of liberal criminal law theory. Part three then explores the three broad areas of the criminal law, and parts four and five carry the debate into the political obligations of individuals and of the State in these matters.