In good condition. 
The only defect being some softening to the engraving due to polishing. 
A large size. The drum is 2.5 inch diameter by 2.35 inch high. Maximum width into handle is 3.8 inch.
Weight is 138 gm without liner and 288 gm with the liner . 
Age1855, Assay office London. 
Silversmiths Arthur Sibley.
Nice shell thumbpice. 
Strong handle. Flat lid. Tight fitting glass liner
This type of mustard pot would have been a luxurious addition to any dining table during the Victorian era