Old silverplate box...Sheffield or?

I have a small silverplate lidded box…about 2 1/2" x 3 1/4" x 1" and it has a hallmark on the bottom which consists of a shield which is about 3/16" across and in it are three symbols which are the standing lion (like a Glasgow mark), crossed keys which I have found are an early Sheffield mark used by three different makers, and a “P” which looks like a date mark. Then under the shield is a number 270 which is also stamped near the hinged edge of the inside of the lid. Copper is showing through by the hallmark and the silver as well as the top rearing lion which is stamped on the top. the silver plate is starting to finely bubble on the top as well and copper is showing through the top lion. Is this early Sheffield or what is it? Thank you very much for any clue!
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It looks like electroplate and is definitely not early Sheffield (by which I assume you mean Old Sheffield Plate). I don’t recognise the manufacturer’s mark, but hopefully somebody more knowledgable will be along soon.

Thanks silvermakersmarks for your input…do you have any guesses as what this might be? I assumed it is British but maybe not? (I’m in the US) And also how does one distinguish between the older plate and electroplating?

Prill Silver Company, New York City.

Old Sheffield Plate (OSP) has a layer of silver fused to the base metal so at the edges it is normally possible to see the separate layers. Electroplate (EP) uses an electrochemical method for depositing a very thin layer of silver on the surface of the base metal. OSP therefore uses much more silver per item than EP which is why it fell out of favour when the cheaper EP method was invented by Elkingtons. The disadvantage of EP for the owner is that the silver wears through to the base much more quickly.

Thank you snuffer! I should have realized it might not be British and I probably could have found the mark in the silver ID site I use.
And also thank you silvermakersmarks for your help also…there is always something new to learn. Much appreciation to you both!
This is a great site too…am glad I found it! :