InR v. W [2010] EWCA Crim 372, [2010] 3 W.L.R. 165, a detective in the Metropolitan Police was accused of fiddling his expenses to the tune of £12,500. For this he was at first successfully prosecuted for the common law offence of misconduct in public office. However, the Court of Appeal then quashed his conviction and ordered a retrial because, in their view, the judge should have told the jury, as he would have done in a trial for theft or fraud, that the detective was not guilty unless he was “dishonest”. Because “dishonesty” (they said) is an ingredient of the offence of misconduct in public office when committed in such circumstances as these, the detective would not be guilty if he genuinely believed that there was nothing wrong in what he did because it accorded with “the culture in the office at the time”, which tolerated false expenses claims, provided the till-dipper intended at some future point to pay the money back.

The decision has been criticised as adding a new and unnecessary complication to the offence of misconduct in public office (Richardson, [2010] Criminal Law Week, 11, §5). But what lay behind the Court of Appeal's decision, surely, was a sense of unease that the policeman had been prosecuted for misconduct in public office rather than for a simple fraud or theft. And their unease was understandable, because it is arguable the offence of misconduct in public office should not cover what the detective did, even if “dishonesty” was present.

The essence of the crime of misconduct of public office is either wilfully neglecting to carry out the public duty entrusted to you, or wilfully abusing it for some improper end. On principle, surely, it ought not to cover the incidental commission of another crime in the course of performing it. Here the policeman's behaviour was just a simple expenses fraud, as might be committed by any dishonest employee. His status as a policeman might be thought to aggravate the sentence for the fraud offence. (In France, indeed, it would do so explicitly, because article 313–2 of the Code pénal raises the maximum penalty for fraud (escroquerie) from five years' imprisonment to seven if the person committing it was a dépositaire de l'autorité public; a provision not required in England, where the maximum penalty even for the basic crime is ten!) But, surely, by fiddling his expenses the policeman in W no more wilfully abused his public office than he would have done if, during working hours, he had driven his patrol car dangerously, or groped an unconsenting WPC.

The point at issue here, surely, is the same as the one that recently arose in a different context in the high-profile case of Chaytor and others [2010] EWCA Crim 1910, where four MPs accused of false accounting in respect of fraudulent expenses claims tried to argue that they were immune from prosecution because their submission of expenses claims was protected by Parliamentary privilege. In rejecting their arguments, the Court of Appeal said:

However, it is difficult to say exactly what behaviour the crime of misconduct in public office does cover because it is a common law offence and – like that of its “civil partner” the tort of misfeasance in public office – its definition is uncertain. And so, like other common law offences, it has a tendency, like ground-elder in a garden, to spread in all directions; and, unless it is kept carefully in check, it will take over anything and everything.

In A G's Reference (No. 3 of 2003) [2005] Q.B. 73 the offence of misconduct in public office was invoked against two police officers who, it was alleged, had neglected a prisoner who died in the cells at the police station, whose life would have been saved if he had received medical attention: a proper case, one would have thought, for a prosecution for manslaughter by gross negligence. In upholding the trial judge's decision to direct the jury to acquit, the Court of Appeal, having wrestled with a body of case-law dating back to 1599, summarised the ingredients of the offence of misconduct in public office thus:

This judicial definition is an improvement on the uncertainty that preceded it, but the resulting offence is still distinctly vague. In particular, this formula does not limit the active form of the offence, as I believe it should be limited, to the improper exercise of the public function, so that it does not extend to behaviour merely incidental to it, like making fraudulent expenses claims.

At the risk of stating the profoundly obvious, the case of W is yet another demonstration of the need for English criminal law to be reduced to a comprehensive statutory code. In the twenty-first century there is surely no room in the criminal justice system of a civilised country for common law offences, the scope of which is vague and ill-defined. But to add another obvious but pessimistic point, unless common law offences are codified carefully and thoughtfully, they are better left alone. When confronted with the new statutory definition of the previously common law offence of conspiracy created by section one of the Criminal Law Act 1977, the late Professor Glanville Williams was heard to say: “I've spent my academic life campaigning for codification – but when I look at this I wondered why I bothered!”