gotta say, if i were a cop, i'd ping people for that too. the whole idea of p plates is that they're visible. you might as well not be displaying them, and hence, a fine for not displaying p plates.
edit:: just show the plates, and sure you might get hassled, but be polite about it. "Yes sir, i understand that you're just checking I'm not driving a restricted vehicle; i made sure to buy a non-turbo. I can show you if you'd like."
srsly guise