Prosecution as in England must only be undertaken if they are required by the public interest. What is this public interest and how is it understood?
Can these decisions not become quite politically loaded? For example, suppose an anti monarchist protestor breaches the public order act. A monarchist sympathetic prosecutor may more likely deem prosecution in the public interest. Suppose a monarchist then assaults him. A republican may deem the protectors prosecution ass contrary to the public interest and the assailant's as required by it.
But that is not really the public interest but rather the interest of a given specific political cause. What is the public interest when it comes to political masters?