You seem to have nailed the hallmark details pretty well although I would suggest that the maker is James Fenton rather than James Fenton & Co (the “& Co” didn’t come until later). 1854 makes this a very early piece of Fenton’s work as his first mark was only registered in April 1852. You have probably worked out what the individual marks actually mean but from left to right:
- lion passant - indicates sterling silver (925 parts pure silver per 1000)
- Queen Victoria’s head - duty mark shows the relevant tax has been paid
- letter F - date letter (note that the assay year did not coincide with the calendar year so what we call 1854 could also be from the first part of 1855)
- anchor - town mark for Birmingham
- JF - maker’s, or more accurately, sponsor’s mark
Knives of this shape could be for fish or butter but I think that, as the fork tines are so short, these are for butter.
Assuming that the fork has matching hallmarks I would suggest that the value is going to be somewhere in the £40-£60 region.