Interesting old tea set, well loved and cared for, in a way. I've never seen a tea set like this before.
When the silver plate on this set became worn, it was neatly polished away, down to the base metals (pewter on the body, pewter or a similar white metal handles and spouts). This looks very professionally done, by a jeweler or a metalcrafter.
Marks are Sheffield Plate - 851. This may have been plated with 851 silver originally, we'll never know, since the silver is gone. It's not the usual Sheffield plate I see, which is silver over copper.
The shape is rather neo-gothic style, with angular handles. And though these pieces are all much used and show it, it's still a lovely vintage set.