Avoiding another Post Office Horizon scandal

Dr Huw Evans, academic lawyer, Cardiff Metropolitan University

The Ministry of Justice (MoJ) is consulting on the ‘oversight and regulation of private prosecutors in the criminal justice system’.

This follows from recommendations in a 2020 House of Commons Justice Select Committee report and against the background of the Post Office Horizon scandal (POHS).

This article discusses two aspects of that consultation: proposals to make private prosecutors, like the Post Office, subject to an inspection regime and to a mandatory code.

An enforceable code could set out principles private prosecutors must follow.

This may sound dry, but effective outcomes can make a future scandal less likely.

Injustice

Such is the industrial scale of the POHS injustice, the Post Office (Horizon System) Offences Act 2024 was passed which automatically quashed victims’ convictions. 589 victims had been identified and had their convictions quashed by February 2025. This figure does not include any quashed since February or convictions previously quashed on appeal.

What is a private prosecutor?

There are public bodies that prosecute such as the Crown Prosecution Service, the Serious Fraud Office or the Health and Safety Executive, who function under a statutory regime including a power to prosecute. A ‘private prosecutor’ is anyone else that prosecutes.

The term ‘private’ is misleading because it can catch public bodies not given a specific power to prosecute, like the Post Office.

Prosecution of offences

In England and Wales there is a general right for a person to bring criminal proceedings against someone else under the Prosecution of Offences Act 1985. The Post Office’s right to prosecute is under the 1985 Act.

The 1985 Act also established the CPS, which took over the conduct of prosecutions from the police.

The change followed from the 1981 Royal Commission on Criminal Procedure report which recommended separation of the investigation and prosecution functions because ‘the investigator, by virtue of [their] function, is incapable of making a dispassionate decision on prosecution’.

Under the 1985 Act the CPS can take over the conduct of proceedings from a private prosecutor but this hasn’t materially happened in practice as evidenced by the POHS.

Prosecutor oversight

CPS performance is scrutinised variously. Its actions can be scrutinised in the High Court through judicial review.

There is a CPS complaints procedure.

The CPS is inspected by His Majesty’s Crown Prosecution Service Inspectorate (HMCPSI). Although HMCPSI can only make recommendations, it is a de facto regulator. Its recommendations carry weight and can be enforced within government.

The head of the CPS, the Director of Public Prosecutions, and the HMCPSI Chief Inspector are both answerable to the Attorney General. The Attorney General is answerable to the UK Parliament.

Private prosecutors do not have that oversight. The consultation addresses this with a proposal to extend inspection to private prosecutions.

The logical position would be to extend the remit of HMCPSI to cover private prosecutors. If this happened, HMCPSI would need to be given appropriate enforcement powers.

In addition, the regime would need to be underpinned by potential sanctions for non-compliance including, where there was proved wrongdoing, disqualification to act as a prosecutor.

If that regime had been in place, potential disqualification of the Post Office as a prosecutor would have been very real.

Prosecutor mandatory codes

There is a mandatory code which governs CPS prosecutions. All prosecutions must be justified by a two-stage test: that there is sufficient evidence and that it is in the public interest.

Having enough evidence might seem obvious but assessing this requires objectivity.

Even if there is sufficient evidence to prosecute, it does not follow automatically that it is in the public interest to prosecute; for example, an accused person might have a terminal illness, or the offence might be trivial.

Again, assessing the public interest requires a dispassionate element.

Because of CPS scrutiny the code can be meaningfully implemented. If it is not, for example, a decision to prosecute or a conviction can be quashed.

Alongside the CPS, there are various private prosecutors including the RSPCA for animal welfare cases, the Federation Against Copyright Theft (FACT) for intellectual property cases and, as we have heard, the Post Office.

Private prosecutors are not subject to a mandatory code. They don’t have to apply the two-stage test, although they might choose to do so.

An MoJ consultation proposal is that private prosecutors should be subject to a mandatory code.

Logically, any mandatory code should be consistent with the CPS code and require the application of the two-stage test.

Combined with an inspection regime, if private prosecutors were subject to a mandatory code, they would be more accountable. There would be a better chance that decisions to prosecute could be justified.

Why not remove the right to private prosecution?

But should there be a general right to bring a private prosecution? Bringing a prosecution impacts on a person’s life. Self-evidently, the impact is far greater if conviction and imprisonment follow, especially if compounded by abuse of process.

The whole range of impact was present in the POHS.

If the Post Office prosecutions had been carried out solely by the CPS, the injustices would more likely have been avoided. Investigation and prosecution could have been separated with dispassionate consideration, the two-stage test could have been properly applied, and there could have been full disclosure of evidence: for example, about flaws in the Horizon system.

As the ‘victim’, the Post Office also had a financial interest in cases’ outcomes. It blurred dispassionate assessment. The CPS would not have had that distraction.

As prosecution is so significant a step, it can be argued that this should be left to the state, in conjunction with appropriate safeguards, such as with CPS oversight.

Private prosecutions are not permitted in some jurisdictions such as Jersey.

Therefore, limiting the right to prosecute to specialist prosecutors like the CPS is a legitimate response to protect against the risk of abuse.

But there is a legitimate alternative argument; if the state fails to prosecute cases where it should, there is a failure in the rule of law. This failure has occurred and been exacerbated by prolonged and continuing reduced resourcing of public prosecutors like the CPS.

In those situations, private prosecutors sometimes step in: for example, the RSPCA with animal welfare cases; or Sky, the Premier League and FACT with intellectual property cases.

Injustice can arise through vexatious prosecution, such as with the POHS, but it can also arise through failure to prosecute even though there is sufficient evidence and prosecution is in the public interest.

Private prosecutions to remain

The second argument has prevailed. The consultation strikes a balance between proportionate regulation to prevent abuse, while not unjustifiably restricting the right to bring a private prosecution.

The devil will be in the detail but proposals for an inspection regime and a mandatory code are sound in principle and can help strike that balance.

Resourcing will be key. A private prosecution inspectorate must have the capacity to be effective.

Making private prosecutors subject to an effective inspectorate and a mandatory code does not guarantee that there will be no future miscarriages of justice like the POHS. But it does make it less likely.