So next time I see an old lady about to be mugged, I won't step in and stop the attack because I'll be obstructing the police in the course of their duty to apprehend the mugger.
At the point of me flashing a warning, the other motorist may not yet have committed the offence, as speed cameras are often sited at a point just after the speed limit changes down. If I can prevent them from committing the offence, I am performing a civic duty.
I repeat. The CPS should be thoroughly ashamed of themselves.

