14k, 18k, FJ Any ideas on the history or maker of this ring please?

by john
(uk)

Any ideas on the history/age or maker of this ring please?

14k 18k F J and what looks like a 'C' with a crown inside and 3mm diamond.white gold? platinum setting around gold band.

so far I am assuming the white gold is 14k and band 18k???

about to give it to my girlfriend as an engagement ring so I was hoping to give a little info with it...
any help would be fab

cheers