Never had the CE plate checked, which is good as mine dosn't have one!
All they have ever asked for was passports and ships papers.
As regards the courtesy flag, I fly it from the forward light mast just below the nav lights. The ensign flies from the stern light mast, just below the aerial and stern light. Not ideal but seeing as I do not have an A frame is the best I can do. A courtesy flag should be hoisted upon entering foreign territorial water, but mid Channel is not the best place to do it so I wait until we have crossed the TSZ. To not fly the flags is as good as poking the Gendarme in the eye and inviting him to watch our Olympics