originally UK maker's marks were pictograms, but by the early 1600s it became a common practice to use the maker's initials. The problem is that there isn't enough information or a photograph of the mark on your Bracelet to go by.
There are a number of registered marks with the letters JP. The shape of the cartouche that the intials appears within are crucial, so is the style of the letter and the shape of the cartouche the date letter appears within. The date letter, in this case the letter "Z" tells you the year the maker's mark was registered but we need to see it.
There is a link to a page where you can research British Hallmarks in the Jewelry Resources.
