This is in the news at the moment and will be for a while. For that reason, we will steer clear of any comment on the facts of that (and any other) allegation, but here’s some background on the offence. As well as the usual disclaimer that is repeated, nothing here should be taken to be a comment about any particular ongoing case (we have in any event no information about them). It is often called ‘misfeasance in a public office’.
Classification – The offence is not defined in statute (an Act of Parliament), it’s what’s called a ‘common law’ offence. For this reason, it is indictable only.
Definition – As there is no act of Parliament, the definition of the offence comes from judgments of the Court over the years. The current defintion comes from Attorney-General’s Reference (No. 3 of 2003)  EWCA Crim 868 :
- The Defendant must hold a ‘public office’ – they must execute some form of public function. A police officer would be, as would be an employee of a local authority (Bowden  Cr App R 104), but not a private employee. It doesn’t matter if the person is being paid (Belton).
- The alleged offence must relate to their public duty.
- He must ‘wilfully neglect to perform his duty and/or wilfully misconducts himself’ – the CPS have some good guidance on this.
- The failure or misconduct must be of such a level as to ‘amount to an abuse of the public’s trust in the office holder.
There must also not be any ‘reasonable excuse of justification. The above questions will all have to be answered by the jury in light of all the circumstances of the case and what conclusions of fact they make. For that reason, it is hard to give much more guidance.
What sort of sentence do you get? – The maximum sentence is life imprisonment, but that would never be passed in practice.
The Court of Appeal gave guidance in relation to police officers after reviewing their previous decisions in the case of R v Bohannan  EWCA Crim 2261. There is no guidance about non-police officers, presumably because there are far fewer prosecutions – not enough to draw any conclusions.
Broadly, it should always attract a custodial (prison) sentence. This is both to deter others and to send a message to the public that those that betray the trust put in them by the public will be punished. Further, if the individual benefits from the offene, then that will aggravate it. A further aggravating feature is if the result of the misconduct is to assist criminals in evading justice, all the more so if it impacts on an on-going operation.