http://www.vikingsword.com/ubb/Forum1/HTML/002441.html
Great find on the "broad arrow" mark, Nathaniel. As I mentioned to you privately, the "BP4" referenced in the HOS catalogue was a mistake--the "4" referred to the arrow mark.
Given the other "___ P" marks I've seen on bayonets, I'm inclined to think the "BP" stands for Burma Police, but that's mostly speculation on my part.
Cheers,
Andrew