Who decides whether to prosecute someone?
In England and Wales, the Crown Prosecution Service (CPS) decides in most cases — not the police, and not the victim. That separation is deliberate and is the point of the arrangement.
Why the CPS exists. Before 1986, the police both investigated and prosecuted. The Prosecution of Offences Act 1985 created an independent prosecuting authority, so that the decision to charge would be made by someone other than the people who built the case. Investigators are not well placed to judge their own work dispassionately.
How the decision is made: the Full Code Test, set out in the Code for Crown Prosecutors, with two stages that must both be satisfied.
The evidential stage. Is there sufficient evidence to provide a realistic prospect of conviction? This means an objective assessment that a reasonable bench or jury, properly directed, is more likely than not to convict. It is an objective test, not a prediction of what a particular jury will do, and it is deliberately not the same as believing the suspect is guilty.
Prosecutors consider whether the evidence is admissible, reliable and credible, and whether there is other material that might undermine the case.
The public interest stage. Only if the evidential stage is passed. Factors include the seriousness of the offence, the suspect's culpability, harm to the victim, the suspect's age and maturity, the impact on the community, whether prosecution is a proportionate response, and whether sources of information require protection. The victim's views are considered but are not determinative — the prosecution is brought in the public interest, not on the victim's behalf, which is why a case can proceed against a victim's wishes and, more painfully, can be dropped despite them.
The Threshold Test applies where a suspect poses a substantial bail risk and not all evidence is yet available.
Exceptions. Police charge some minor offences themselves. Other bodies prosecute in their own fields — the HSE, the Environment Agency, local authorities, the Serious Fraud Office. Private prosecutions are possible, though the DPP can take them over and discontinue them.
Challenging a decision: the Victims' Right to Review scheme allows a review of a decision not to charge.
General information, not legal advice.