Antique Silver Hallmarked British Pocket Watch

Silver hallmarked British fusee pocket watch with a key

This beautiful large and heavy pocket watch is in working condition
55 mm in diameter - 20 mm thickness

The face and movement is marked with the name A. Otty from Halifax
The movement and inner case is marked with 20771
(There is a small mark in front of this serial number which looks like a tax duty mark -
used between 1837 and 1890) 

The outer case is marked with:
The town mark of London (assay office)
The lion to certify the silver quality
The makers mark W.H could be
William Hammon from Coventry (1876 to 1885) - (we are not sure)