Question I have, does your typical plod actually know this or not?
Doesn't really matter, apart from the inconvenience of being pulled over. I remember being pulled over on my chop donkeys years ago. The cop was determined to find something to do me for. He finally said said, "aha, you haven't got a chain guard!" I said "do I need one?" He didn't know, so begrudgingly let me go
Some definitely don't
A few years ago I replaced the number plate on muffin just because it had started to look tatty , I bought it online because most shops now only stock and make the large plates up, it was bought as a legal plate but was smaller because of only having 5 digits , it had the makers postcode and the bs number on it as well. The next night a group of us were riding to Willingham woods bike meeting place and the Police were pulling in as many bikes as they could for number plate checks and warnings, first mate had bog standard plate on and was told to go , next mate had a small illegal size plate and was just told to change it , then it was my turn and the officer said your plates illegal change it or next time we will prosecute . I pointed out it was brand new and had been bought as a legal plate 2 days before ( I even had to send documents to get it made ) So I asked him why , first reply was it was too small so I pointed out the legal requirements on font size and borders etc , next it was because there wasn't the correct spacing between the X and the 1 , I again pointed out the legal requirement was met. It was then that he had been doing this job for years and could tell it was illegal but seeing as it was just a warning to leave
I refused to go until he proved to me why it was illegal so his next excuse was that the font of the letter B was illegal because it had a small tail to the left at the top and bottom of the B , I pointed out it was a standard font so his reply is no it's not it should be the same as on his police car , so we had a look and his font was identical to mine so he asked me to leave again.
I told him I needed to know so I could contact the supplier that had sold me it as a legal plate , his answer is they tell you that to get your money , I pointed out that they don't put their identification number required by law if it's illegal though. He gave up before me and after about 25 minutes just walked off .................. my mates were amazed that he never mentioned my 116db Buell race exhaust system out to me as well