A-Z of British Etiquette
A skilled society darling will know that these are only eaten in months containing the letter R. The upmarket way to eat is to simply tip the contents into the mouth from the shell, having loosened the contents before with a fork.
An oyster fork is a Victorian middle-class invention and does nothing a normal fork cannot already do. If an oyster fork is set, use it. If not, just use a normal small fork. Never ask for an oyster fork or that will set you into a class of your own. Cattle class!