Let's say an alleged fraud somehow passed the evidential test. Either the WG admitted that anal was offered and payment included that and that it wasn't given, or some DNA can show anal did not occur. But there is one way or another enough evidence. At that stage the police (using the same tests as the CPS) must ask if it is likely to satisfy the public interest test.
Some of the formal factors the police may consider include a) seriousness of the offence b) suspect’s level of culpability c) circumstances of and harm caused to the victim d)impact on the community e) whether prosecution is a proportionate response, eg, is a nominal penalty likely? (I've missed a couple out that seem not to be relevant here).
You could end up, as is often the case, where the evidence shows that a crime has been committed but that a decision not to prosecute is made in the public interest.
Imagine the older days in say Glasgow. A bobby collars a skank who has not provided all the services promised. He is convinced the punter is telling the truth and suggests the girl gives him back a fiver. She reluctantly agrees mostly as she wants to stay on good term with the police. Justice is served and thousands of pounds of tax-payer's money saved. Hypothetical but not unimagineable in the days when the police did their job in Glasgow protecting both punters and streetwalkers.
