Its the font size that is the issue not how many lines its on. The font has to be as it was from the dealer and the letter/number size should be as it left the showroom. If you want i can find the size. ANPR will rear the letters no matter what order they are in single row or one line above the other.
The penalty for a plate varies depending on where you are, it used to be a VDRS (get it changed Mot garage to stamp form and post the slip off within 14 days) Some go for a £60 fixed penalty notice no discretion. Some forces are now not letting the cop on the street make the decision but a person in an office who has not seen the plate make the decision.
Some cops may just have a word in your ear and send you on your way, i think this depends how small the plate is, and if the cops a biker. A had a cop on a bike pull a ruler out of his boot to measure the letters on my plate then use this as his evidence.
I like my plate to be seen- if the bike gets nicked i want a camera and cops to see the plate. ANPR would read a correct size plate if its too small it may not get a clear rear.