The marks are not hallmarks. Hallmarks are marks struck by an official assay office, what you have here are marks struck by the maker only, they imitate to some extent, English hallmarks. They are just Charles Catton's way of indicating that the ladle is made of silver, but as to the standard of silver, that would have to be tested.
Much depends on the reputation of the silversmith, the ladle may have been made out of coins, or other old silver and I dare say he would only have a rough idea of the standard. It was common at these times to take old silver, in whatever form, to the silversmith to have something useful made up.