Hello again,
Marks do not match at all. There is Swiss ``grouse `` mark used 1882 – 1934 for .800 standard, as well as .800 mark.
Then we have ``lion passant`` for sterling fineness (.925) and date letter ``U`` that does not match any year in 19th century:
https://www.silvermakersmarks.co.uk/Dat ... s%20U.html In conclusion, this watch case was not legally assayed at London Assay Office (leopard`s head).
For Merchandise Marks Act introduced to protect the British watch trade in 1887 take a look here.
viewtopic.php?t=12960Regards