Hi Graham
Interesting mark. I have a buckle frame dating to c1770 with a very similar,if not identical makers mark of PP.
My buckle was literally dug up (by a metal detectorist) at Chester racecourse, and has no Lion Passant. I concluded it MAY be Peter Pemberton III of Chester.
At Chester the first ,now unindexed plate 1 , covers 1701 -1841 and has several unrecognised marks - one of which may be this PP , and thus it may therefore be Peter Pemberton III who according to Jackson (page 406) in 1756 either registered a mark or became a member of the Chester Goldsmith's Company.
Curiously the assay mark seems to be a Lion Passant rather than a Lion Passant Guardant, but thats probably odd wear .
see
viewtopic.php?f=48&t=17617&p=39663&hilit=peter+pemberton#p39663