You don't prosecute criminal cases. The crown prosecution service does. If you're attacked and theres sufficient other evidence or witness statements as evidence, and its deemed to be in the public interest to do so then its absolutely right that you be tried for it.
If your statement is needed in a court then you are able to be compelled to do so.
Both of the above a fundamental principles of a sensible judicial system. The police have nothing to do with whether a case is tried or not.