I can't seem to find anything about the maker "JP" in an octagon from 1900s-1910s. The mark appears to be only on spoons, as far as I can tell.
Any ideas?
I have not found this mark in any of my references. However near-identical marks were used by John Pinches Ltd with London hallmarks from the mid 20th century (I have seen one with a 1948 hallmark). John Pinches himself registered a JP mark in 1897 and in 1912 (the date of your hallmark) is listed in a trades directory as a medallist, die sinker, seal engraver, press & stamp maker, none of which trades sound particularly likely for a spoon seller. However he may have contracted with a Birmingham company for spoons to retail from his business.
I suspect that the only way of confirming an identity for JP is to contact the Birmingham Assay Office directly.