I'm still very much in the learner stage as a new collector of folding fruit knives, but here are some observations that might be helpful.
* I'm going to venture that the knife markings you show indicate that it was probably made by Albert Coles, one of (along with Gorham, et al) the major producers of these knives. They were based in New York City between 1835-1877. The British silversmiths were subject to strict regulations that required them to indicate in registered hallmarks things like the city of assay (e.g. Birmingham's was an anchor), a monarch's head to indicate duty had been paid, maker's marks, and date of assay/manufacture. American silversmiths for the most part had no such regulations to worry about throughout most of the mid-19th century. And, given the lack of agreements between England and the US, American silversmiths often routinely imprinted "faux hallmarks" that mimicked English ones. Your knife shows faux hallmarks of Birmingham and a monarch. What was distinctive of American, and in particular Albert Coles, was the use of the eagle in its stamped markings.
* Albert Coles was a big company and was known to produce knives for other, smaller silversmiths. So--and here I'm speculating--when they did so, I'm guessing they left off their identifying brand stamp, A/C, and replaced it my some other mark that would indicate to them the company they produced the knife for, here an eagle stamp. Here is a good illustration of Albert Coles' distinctive hallmark: http://www.chineseargent.com/home/maker-c-4
* Another characteristic feature of American folding fruit knives is the use of the "French fingernail nick," the long groove at the top of the blade to facilitate opening. The English knives have very short ones.
* My guess is also that the simple, but strikingly realistic representation of fruits (pears, pineapple, etc.) reflects the American silversmith's adoption of the Aesthetic style that became an avant garde reaction to the stuffy and formalistic Victorian style around the middle of the 19th century. Your knife's a beauty, a true work of art.
* Again, since American silversmiths were under no obligation to indicate the purity of the silver used, and this knife has no marks indicating otherwise, it is presumable made of "coin" silver, which can range in purity from 700-900/1000 vs. English sterling 925/1000.
* If you're interested in researching more, here are some publications I've found helpful:
_Pocket Fruit Knives_, by Simon Moore (probably the definitive book covering French, American and some European folding fruit knives
_Silver Folding Fruit Knives_, a booklet by Bill Karsten
_Silver Bladed Folding Fruit Knives_, also a booklet size publication, by D. Hall
Hope that's helpful!