Thats true man, that always happens. I've had a fine for not having p plates up driving my mums car ages ago, but that was through a booze bus, and that was because they are in front of their colleagues they have to press you harder.
Nonetheless its a shit situation to be in. I'm sure we'd all like to drive without them on but for money sake and demerit sake I keep them up. (the f**kers always fall down anyway, bluetack is shit)