I believe you've hit the nail squarely on the head Mick. No policeman - no evidence
However, while I agree that these offences are rife and need to be dealt with, I'm not happy at all with the decision regarding careless driving being handed to the police officer on the spot. Judge, jury and executioner.
I am aware that this is not the case and the fixed penalty notice, as with any other, is merely an invitation to close the matter by payment and endorsement, but in reality, how many people will see it like that? How many people will simply pay up because the police officer says so or, in the (mistaken) belief that it'll cost more to take it to Court?