Student or Learner
I was caught by a policeman on my way back home when I was driving due to speeding. Or, by a police officer?
Well, I guess it should be the police officer...
"Policeman" is dated because it is now considered sexist and therefore politically incorrect by many. A police officer may equally well be a man or a woman.
Speakers of BrE have a nice alternative in "constable". As far as I know constable does not have any sexist connotations.