The four squarish punches on the right may contain the Gothic letters 'EPBM' Electro Plated Britannia Metal.
See:
http://www.925-1000.com/silverglossary2.html
I'm not aware of the identity 'G & C G', but the position of the lower 'G' may not necessarily indicate the maker's surname, but may perhaps indicate the town of manufacture, eg. Glasgow.
Trev.