CopperCyclist
Veteran
So would the next step be - who has an alibi at the time, or does it just get dropped? If it does get dropped, who decides that - the PC, Sergeant, Inspector, CPS?
The next steps vary from case to case, but simply put, yes - if there is a way to try and prove who was driving by questioning, then those questions will be asked. The problem is that it's very easy to give an untruthful answer which is impossible to disprove to the burden required by the court.
Different forces will have different policies as to who chooses to drop it, but a usual approach would be for a PC to write up the report explaining everything they've done, and why they think they can't go any further. A sergeant would then check the report and agree, or suggest further lines of enquiry if they spot something that was missed.
In this instance, it would appear PC and PS decided to actually report the driver to court, hoping that a court would choose to believe they are lying. Once the matter is at court in this way, it's then CPS that make the choice to discontinue as they were certain that the drivers excuse would result in a not guilty.