Hi Robert, I'm far from being an expert but know a little bit. The Mappin stamp is almost certainly the maker (or retailer), correct.
But assuming it is silver plated and not silver the rest is unfortunately just gobbledygook designed to look like a hallmark.
This was common practice back in the day. Makers of quality silver plate items stamped faux hallmarks on them so that buyers who could not afford solid silver could still impress friends and guests who usually wouldn't know any different.
Sent from my SM-A105FN using Tapatalk