C&MK Cunningham & McKensie, 1785

[Granmaa]

I checked the Edinburgh Assay Office database for this mark, and although it doesn't have this exact mark, it does have a C.MK which it lists it as provincial, unidentified.
There seems to be a good match for it in Jackson's (no mark illustrated), where it lists a Cunningham & McKenzie, first mentioned 1784.

Miles