Quiet Street Antiques of Bath has dated this piece to the 1870s.
The original 54-hour fusee movement with chronometer escapement features gold hands and a silvered engraved dial signed: "John Poole, maker to the Admiralty, 57 Fenchurch Street, London." Subsidiary seconds dial; "Up-and-Down dial and original 'tipsy' winding key.

John Poole was a chronometer maker of considerable note; the dial shows the firm won a gold medal in 1867 ~ and as the business moved from Fenchurch Street (after John Poole's death in 1870) this can be dated precisely within those three years.
Quiet Street Antiques of Bath has dated this piece to the 1870s.
Fine antiques at sensible prices
You can view the stock and full dealer information on the Quiet Street Antiques of Bath Profile Page