You may or may not find this interesting. This is an extract from the Code for Crown Prosecutors, in respect of whether they should prosecute or not. I would imagine that this is much the same for service police, although as always I am open to correction.
5 THE FULL CODE TEST
5.1 The Full Code Test has two stages. The first stage is consideration of the evidence. If the case does not pass the evidential stage it must not go ahead no matter how important or serious it may be. If the case does pass the evidential stage, Crown Prosecutors must proceed to the second stage and decide if a prosecution is needed in the public interest. The evidential and public interest stages are explained below.
THE EVIDENTIAL STAGE
5.2 Crown Prosecutors must be satisfied that there is enough evidence to provide a ‘realistic prospect of conviction’ against each defendant on each charge. They must consider what the defence case may be, and how that is likely to affect the prosecution case.
5.3 A realistic prospect of conviction is an objective test. It means that a jury or bench of magistrates or judge hearing a case alone, properly directed in accordance with the law, is more likely than not to convict the defendant of the charge alleged. This is a separate test from the one that the criminal courts themselves must apply. A court should only convict if satisfied so that it is sure of a defendant’s guilt.
5.4 When deciding whether there is enough evidence to prosecute, Crown Prosecutors must consider whether the evidence can be used and is reliable. There will be many cases in which the evidence does not give any cause for concern. But there will also be cases in which the evidence may not be as strong as it first appears. Crown Prosecutors must ask themselves the following questions:
Can the evidence be used in court?
Is the evidence reliable?
5.5 Crown Prosecutors should not ignore evidence because they are not sure that it can be used or is reliable. But they should look closely at it when deciding if there is a realistic prospect of conviction.
THE PUBLIC INTEREST STAGE
5.6 In 1951, Lord Shawcross, who was Attorney General, made the classic statement on public interest, which has been supported by Attorneys General ever since: “It has never been the rule in this country — I hope it never will be — that suspected criminal offences must automatically be the subject of prosecutionâ€. (House of Commons Debates, volume 483,
column 681, 29 January 1951.)
5.7 The public interest must be considered in each case where there is enough evidence to provide a realistic prospect of conviction. Although there may be public interest factors against prosecution in a particular case, often the prosecution should go ahead and those factors should be put to the court for consideration when sentence is being passed. A
prosecution will usually take place unless there are public interest factors tending against prosecution which clearly outweigh those tending in favour, or it appears more appropriate in all the circumstances of the case to divert
the person from prosecution (see section 8 below).
5.8 Crown Prosecutors must balance factors for and against prosecution carefully and fairly. Public interest factors that can affect the decision to prosecute usually depend on the seriousness of the offence or the circumstances of the suspect. Some factors may increase the need to prosecute but others may suggest that another course of action would be better. The following lists of some common public interest factors,
both for and against prosecution, are not exhaustive. The factors that apply will depend on the facts in each case. Some common public interest factors in favour of prosecution
5.9 The more serious the offence, the more likely it is that a prosecution will be needed in the public interest. A prosecution is likely to be needed if:
a a conviction is likely to result in a significant sentence;
b a conviction is likely to result in a confiscation or any other order;
c a weapon was used or violence was threatened during the commission of the offence;
d the offence was committed against a person serving the public (for example, a police or prison officer, or a nurse);
e the defendant was in a position of authority or trust;
f the evidence shows that the defendant was a ringleader or an organiser of the offence;
g there is evidence that the offence was premeditated;
h there is evidence that the offence was carried out by a group;
i the victim of the offence was vulnerable, has been put in considerable fear, or suffered personal attack, damage or disturbance;
j the offence was committed in the presence of, or in close proximity to, a child;
k the offence was motivated by any form of discrimination against the victim’s ethnic or national origin, disability, sex, religious beliefs, political views or sexual orientation, or the suspect demonstrated hostility towards the victim based on any of those characteristics;
l there is a marked difference between the actual or mental ages of the defendant and the victim, or if there is any element of corruption;
m the defendant’s previous convictions or cautions are relevant to the present offence;
n the defendant is alleged to have committed the offence while under an order of the court;
o there are grounds for believing that the offence is likely to be continued or repeated , for example, by a history of recurring conduct;
p the offence, although not serious in itself, is widespread in the area where it was committed; or
q a prosecution would have a significant positive impact on maintaining community confidence.
Some common public interest factors against prosecution
5.10 A prosecution is less likely to be needed if:
a the court is likely to impose a nominal penalty;
b the defendant has already been made the subject of a sentence and any further conviction would be unlikely to result in the imposition of an additional sentence or order, unless the nature of the particular offence requires a prosecution or the defendant withdraws consent to
have an offence taken into consideration during sentencing;
c the offence was committed as a result of a genuine mistake or misunderstanding (these factors must be balanced against the seriousness of the offence);
d the loss or harm can be described as minor and was the result of a single incident, particularly if it was caused by a misjudgement;
e there has been a long delay between the offence taking place and the date of the trial, unless:
• the offence is serious;
• the delay has been caused in part by the defendant;
• the offence has only recently come to light; or
• the complexity of the offence has meant that there has been a long investigation;
f a prosecution is likely to have a bad effect on the victim’s
physical or mental health, always bearing in mind the
seriousness of the offence;
g the defendant is elderly or is, or was at the time of the offence, suffering from significant mental or physical ill health, unless the offence is serious or there is real possibility that it may be repeated. The Crown
Prosecution Service, where necessary, applies Home Office guidelines about how to deal with mentally disordered offenders. Crown Prosecutors must balance the desirability of diverting a defendant who is suffering
from significant mental or physical ill health with the need to safeguard the general public;
h the defendant has put right the loss or harm that was caused (but defendants must not avoid prosecution or diversion solely because they pay compensation); or
i details may be made public that could harm sources of information, international relations or national security.
5.11 Deciding on the public interest is not simply a matter of adding up the number of factors on each side. Crown Prosecutors must decide how important each factor is in the circumstances of each case and go on to make an overall assessment.
The relationship between the victim and the public interest
5.12 The Crown Prosecution Service does not act for victims or the families of victims in the same way as solicitors act for their clients. Crown Prosecutors act on behalf of the public and not just in the interests of any particular individual. However, when considering the public interest, Crown Prosecutors should always take into account the consequences for the
victim of whether or not to prosecute, and any views expressed by the victim or the victim’s family.
5.13 It is important that a victim is told about a decision which makes a significant difference to the case in which they are involved. Crown Prosecutors should ensure that they follow any agreed procedures.
I am sorry that this is a very wordy post, but I hope it illustrates the complex thinking that goes on before a decision to prosecute is taken. I would imagine that if there was a particular offence and the decision was being taken whether to prosecute or not, the service police would take the advise of their Staff Legal Advisor, who is a qualified barrister. The ultimate decision whether to prosecute at CM is taken by the Naval Prosecuting Authority.