The 'Victorian Lozenge, dating Patented Model registrations
Glass notes: key to lozenges
Registered Design numbers
Class of Material = I – Metal.
Parcel - 1.
Your second photo shows the diamond lozenge registry mark, used from 1842 to 1883:
This design appears to have been registered on Sept. 28, 1863. (There’s a typo on one of the charts on the cited page, which shows 1853 with two different date letters - one of them should be 1863, instead.)
To be clear, this is not a mark found on sterling silver, which would have true U.K. hallmarks. This is a silverplated piece.